Currently, commercial LEDs based on AlGaInN emit light efficiently from the ultraviolet-blue to the green portion of the visible wavelength spectrum. Data are presented on AlGaInN LEDs grown by organometallic vapor phase epitaxy (OMVPE). Designs for high-power AlGaInN LEDs are presented along with their performance in terms of output power and efficiency. Finally, present and potential applications for high-power AlGaInN LEDs, including traffic signals and contour lighting, are discussed.

The external efficiency of conventional light-emitting diodes (LED's) is limited by total internal reflection at the semiconductor-air interface. For conventional GaAs-based LED's, this results in an extraction efficiency of 2%. In non- resonant cavity (NRC) LED's, this problem is overcome by a combination of internal scattering at a textured top surface and reflection on a back mirror, which increases the probability of escape. Using this approach, we demonstrate external quantum efficiencies of up to 40% without encapsulation of the LED. To gain a more detailed understanding of the out-coupling mechanisms in NRC-LED's, the scattering properties of the textured surface are investigated experimentally. The optimum surface texture is found to randomize the direction of the internally reflected light almost perfectly. In addition, NRC-LED's also enables the enhancement of the external quantum efficiency for small and fast LED's. With efficiencies of about 15%, we demonstrate bitrates of more than 1.3 GBit/s. In order to modify the lambertian output characteristics, we have successfully applied microlenses, allowing 50% coupling efficiency into optical fibers with NA equals 0.5.

The GaN-based MQW laser diodes have been improved excellently by introducing GaN/GaInN optical-guiding. The continuous wave laser operation at room temperature has been achieved at the wavelength of 410 nm. The lifetime of room temperature continuous wave operation is longer than 60 minutes at around 1 mW output. The external efficiencies of GaInN/GaN MQW blue and green light emitting diodes (LEDs) have been increased by newly developed flip-chip (FC) type LED lamp structure. The luminous intensities of the FC-type blue and green LEDs were typically 6 cd and 14 cd at 20 mA, respectively. The FC-type blue and green LEDs are the brightest levels in the world currently. The peak wavelengths and full widths at half maximums were typically 464 nm and 27 nm for the blue LEDs, and 515 nm and 32 nm for the green LEDs.

White light for illumination can be produced from LEDs either by combining red, green and blue emitting chips in one lamp, or by using phosphors to down-convert the emission of short wavelength emitting InGaN LEDs. Both concepts will be critically reviewed, and simulations compared with experimental evaluations. As expected, each solution has advantages, but also drawbacks, which are weighted by the specifics of the applications. The overall picture strongly depends on the efficiencies of the single color chips, the temperature coefficients of all involved materials, and the wanted light output per lamp.

10We have investigated efficient light outcoupling from light- emitting diodes (LEDs) by introducing lateral tapers. The concept is based on light generation in the very central area of a circularly symmetric structure. After propagating between two highly reflecting mirrors light is outcoupled in tapered mesa region. By proper processing we achieve quantum and wallplug efficiencies of almost 30% for outcoupling via a planar surface or, respectively, 45% and 44% for encapsulated devices.

In this paper, we overview several of the critical materials growth, design and performance issues for nitride-based UV (less than 400 nm) LEDs. The critical issue of optical efficiency is presented through temperature-dependent photoluminescence studies of various UV active regions. These studies demonstrate enhanced optical efficiencies for active regions with In-containing alloys (InGaN, AlInGaN). We discuss the trade-off between the challenging growth of high Al containing alloys (AlGaN, AlGaInN), and the need for sufficient carrier confinement in UV heterostructures. Carrier leakage for various composition AlGaN barriers is examined through a calculation of the total unconfined carrier density in the quantum well system. We compare the performance of two distinct UV LED structures: GaN/AlGaN quantum well LEDs for (lambda) less than 360 nm emission, and InGaN/AlGaInN quantum well LEDs for 370 nm less than (lambda) less than 390 nm emission.

High power light emitting diodes (LEDs) are of interest for many lighting applications. Flux improvements can be achieved by scaling conventional chips to larger dimensions. However this scaling results in a decrease in extraction efficiency. These penalties can be offset by modifying the chip geometry such that the number of internal reflections is reduced, thereby increasing the probability of photon escape. LEDs with a truncated-inverted-pyramid (TIP) geometry have been fabricated and packaged. Peak efficiencies exceeding 100 lm/W have been measured (100 mA dc, 300 K) for orange ((lambda) _p approximately 610 m) devices. In the red wavelength regime ((lambda) _p approximately 650 nm), peak external quantum efficiencies of 55% (100 mA dc, 300 K) have been achieved. Flux exceeding 65 lumens from a single 594 nm device has also been demonstrated. These characteristics match and/or exceed the performance of many conventional lighting sources.

A new white light emitting diode, the photon recycling semiconductor light emitting diode (PRS-LED) is demonstrated. The device consists of a GaInN/GaN LED emitting in the blue spectral range and an AlGaInP photon recycling semiconductor emitting at the complementary color. Thus the PRS-LED has two emission peaks, one in the blue and one in the amber wavelength range. The theoretical luminous performance of the PRS-LED exceeds 300 lm/W, higher than the performance of phosphor-based white LEDs.

Increasing optical power and electrical-to-optical conversion efficiency enable visible light-emitting diodes to advance into new applications and wider markets. InGaAlP/GaAs and InGaN/sapphire material systems cover the whole visible spectrum of saturated colors used for display, signage, and automotive use. A combination of blue InGaN LEDs with phosphor delivers a 'white' spectrum adequate for most lighting needs. Demand for high optical power requires larger chips suitable for high-current operation. Current crowding effects and their negative consequences for chip performance and reliability limit the performance of high-power chips based on both material systems. Despite the differences between InGaAlP/GaAs and InGaN/sapphire chip structures, a number of common design concepts leading to higher external efficiency and total luminous output have been proposed, including large chips operating at high drive currents. This paper highlights fundamental current spreading and reliability issues related to the chip size and operating current density, outlines a framework for quantitative analysis, proposes and compares a number of novel high-power chip designs.

Monolithic top-emitting resonant cavity light-emitting diodes (RCLEDs) have been fabricated by solid-source MBE. The RCLEDs in the 650-nm range, with modulation bandwidths exceeding 180 MHz, are possible low-cost transmitter candidates for systems using plastic optical fibers (POFs), such as IEEE-1394 at 100 Mb/s and 200 Mb/s and ATM at 155 Mb/s. Modulation bandwidth of greater than 120 MHz and light power of 2 mW (cw) have been achieved for ^(phi )84-micrometer devices driven at a 40 mA current. Accelerated aging tests for 27,500 device-hours indicate no degradation in output power. A variation in device temperature significantly modifies the far-field pattern and thus the fiber coupling efficiency, due to a cavity detuning effect. The effects of detuning and the temperature and bias dependencies of the devices are investigated. The 880-nm RCLEDs have a maximum output power of 25 mW. Applications include open-air optical communication systems, collision avoidance and measurement systems.

A study of the gain-switching process in GaInN MQW laser diodes is reported. Single peak gain-switched optical pulses with pulse widths less than or equal to 40 ps and optical powers equal to 100 mW are observed when electrical pulses with duration of 800 ps are applied. Sub-nanosecond optical pulses with peak powers in excess of 450 mW are also obtained and degradation mechanisms are analyzed. The transient response characteristics of the laser diodes are studied in both the time and spectral domains.

Normal incidence reflectivity measurements were carried out in an AIX 2000G3HT Multiwafer Planetary Reactor^R MOVPE system, a large scale production tool for GaN-based devices, and in the single wafer AIX 200 RF system. In situ monitoring was used to investigate nucleation behavior, temperature dependence of GaN growth, and the deposition of GaN/InGaN multiquantum wells, especially the quality of interfaces. The obtained results were compared with RT photoluminescence, and high resolution X-ray measurements. The optimized SQW and MQW structures were embedded in Si and Mg doped cladding layers. Contacting the layers with simple metal electrodes without any contact processing results in an intense green electroluminescence. Electroluminescence test structures emitting at 540 nm show minimum forward voltages around 4V with a current of 20 mA. Since no contact technology is applied this is a proof of high p-type doping and excellent structural properties of the InGaN. We found a standard deviation of the wavelength at about 533 nm of less than 1% across the wafer. Since these results were reproducibly obtained for structures emitting in the blue or green the basic demands of a reliable production equipment are fulfilled: (1) high precursor yield (typical 20% for the Ga source) (2) uniformity of electrical and optical performance (3) demonstration of electroluminescence with high efficiency.

We have used time-resolved photoluminescence (PL), with 400 nm (3.1 eV) excitation, to examine In_xGa_1-xN/GaN light- emitting diodes (LEDs) before the final stages of processing at room temperature. We have found dramatic differences in the time-resolved kinetics between dim, bright and super bright LED devices. The lifetime of the emission for dim LEDs is quite short, 110 plus or minus 20 ps at photoluminescence (PL) maximum, and the kinetics are not dependent upon wavelengths. This lifetime is short compared to bright and super bright LEDs, which we have examined under similar conditions. The kinetics of bright and super bright LEDs are clearly wavelength dependent, highly non-exponential, and are on the nanosecond time scale (lifetimes are in order of 1 ns for bright and 10 ns for super bright LED at the PL max). The non- exponential PL kinetics can be described by a stretched exponential function, indicating significant disorder in the material. Stretched exponential lifetimes are consistent with a distribution of lifetimes. Typical values for (beta) , the stretching coefficient, are 0.45 - 0.6 for bright LEDs, at the PL maxima at room temperature. We attribute this disorder to indium alloy fluctuations. From analysis of the stretched exponential kinetics we estimate the potential fluctuations to be approximately 75 meV in the super bright LED. Assuming a tunneling based hopping mechanism, the average distance between indium quantum dots in the super bright LED is estimated to be 20 Angstrom.

Variable angle spectroscopic ellipsometry (VASE) and micro Raman scattering have been employed to study the optical anisotropy and optical constants of AlN films grown at high and low temperature (HT and LT). The AlN films were grown by metalorganic vapor phase epitaxy (MOVPE) and molecular beam epitaxy (MBE) on c-plane sapphire ((alpha) -Al₂O₃) substrates, respectively. Anisotropic optical phonon spectra of AlN have been measured along two directions so that the optical axis <c> of AlN is either perpendicular or parallel to the polarization of the incident beam. Nonzero off-diagonal elements A_ps and A_sp of Jones matrix in the reflection VASE (RVASE) measurements indicate that the <c> of AlN is slightly away from surface normal due to substrate miscut. The ordinary optical constants of both HT AlN have been determined spectroscopic ellipsometry at small angles of incidence so that the extraordinary response is greatly reduced. The film thickness along with the surface overlayer was determined via the VASE data analysis as well.

The optical property and microstructure of InGaN/GaN MQW before and after annealed has been investigated by using photoluminescence (PL) and Transmission Electron Microscope (TEM) technique. The photoluminescence intensity of InGaN/GaN MQW LED annealed within AlN powder can be enhanced by 5 times compared with the as-grown one. The diffused Al converted the InGaN/GaN into AlGaN/InGaN. Less dislocation density in the annealed film and more carrier collection ability due to the band gap difference between InGaN/GaN and InGaN/AlGaN can be applied to explain the astonished result. This simple process can improve the optical property of GaN/InGaN QW LED without spending heavy cost in thin film growth.

The basic optical properties of low temperature plasma enhanced chemical reactionary sputtered (PECRS) InN thin films are presented. Optical absorption and reflectance spectra of InN polycrystalline films at room temperature in visible and near infrared (NIR) regions were taken to determine direct band gap energy (2.03 eV), electron plasma resonances energy (0.6 eV), damping constant (0.18 eV), and optical effective mass of electrons (0.11). In addition the UV and visible reflectance spectra have been used to reproduce accurately dielectric function of wurtzite InN for assignments of the peak structures to interband transitions (1.5 - 12.0 eV) as well as to determine dielectric constant (9.3) and refractive index (>3.0). The revealed reflectance peaks at 485 and 590 cm^-1 respectively in IR spectra are connected with TO and LO optical vibration modes of InN films. Some TO (485 cm^-1) and LO (585 cm^-1) phonon features of indium nitride polycrystalline films on ceramics were observed in Raman spectra and also discussed. The excellent possibilities of InN polycrystalline layers for potential application in optoelectronic devices such as LEDs based InGaAlN and high efficiency solar cells are confirmed.

Optical properties of undoped InGaN/GaN multiquantum wells (MQWs) have been investigated by photoconductivity, photoluminescence, and photoluminescence excitation measurements. We report the first observation of persistent photoconductivity (PPC) in InGaN/GaN MQWs and show that the PPC effect arises from In composition fluctuations in the InGaN well layer. From the analysis of the decay kinetics, the localization depth caused by composition fluctuations has been determined. Compared with the results of complementary absorption and photoluminescence measurements, it is found that the quantum-confined Stark effect due to piezoelectric field and composition fluctuations both exist in the InGaN/GaN MQWs. These two effects are responsible for the photoluminescence Stokes' shift in the InGaN well layers. Here, we provide an unique way to distinguish the individual contribution to the Stokes' shift for the piezoelectric field and composition fluctuations.

InAs/InAsSb SQW LED's incorporating AlAs_0.02Sb_0.98 or In_0.83Al_0.17As electron confining barrier layers are reported. Devices emitting 108 (mu) W and 84 (mu) W at 300 K with QW emission at (lambda) equals 4.1 micrometer and (lambda) equals 4.7 micrometer exhibit quantum efficiencies that are improved by factors of 7 and 3.4 respectively over control samples without the barrier. The operating wavelength of negative luminescent (NL) devices with InAs/In(As,Sb) strained-layer-superlattice (SLS) active regions has been extended to (lambda) equals 6.8 micrometer. NL performance is limited by leakage currents that originate in the n+ contact layer.

Native Oxide AlAs layer were employed to block the current injection from the top anode. The luminous intensity exceeded 75 mcd of the LED chip with native oxide. AlAs layer sandwiched 5 micrometer AlGaAs current spreading layer under 20 mA current injection. Electrical and optical properties the LED chip and plastically sealed lamp were measured. Aging of the LED chip and lamp were performed under 70 degree Celsius and room temperature. Experiment results shown that there is no apparent effect of the native oxided AlAs layer and the process on the reliability of the LED devices.

Current developments in computer technology give rise to increasing data communication over relatively short distances at backplane- and inter MCM interconnect level. It is foreseen that electrical interconnect will not be able to accommodate the necessary data traffic in advanced data processing systems in the future and hence a bottleneck will be created. A potential remedy for this interconnect problem is the use of parallel optical datalinks. In this paper we propose small diameter step index plastic optical fiber ribbons in combination with high efficient resonant cavity LED's as a cheap and feasible option for these optical links. A design for such an optical link is presented with special attention for the optical pathway. Experimental results on the optical properties of the used POF are shown. We describe the development of RCLED's at 850 nm specially designed for efficient coupling into POF. We measured a RCLED to POF coupling efficiency up to 40%. Additionally we report on the technologies used for the fabrication and assembly of the optical pathways and finally some experiments were carried out on the first realized assemblies.

We present detailed studies of polymer light emitting diodes fabricated from ionically self-assembled monolayer thin films. The ionically self-assembled monolayer (ISAM) films are created with a new thin film fabrication technique that allows detailed structural and thickness control at the molecular level. The ISAM fabrication method simply involves the dipping of a charged substrate alternately into polycationic and polyanionic aqueous solutions at room temperature. Importantly, the ISAM technique yields exceptionally homogeneous, large area films with excellent control of total film thickness. Our studies concentrate on improving the performance of ISAM light emitting diodes that include poly(para-phenylene vinylene) (PPV). The individual thickness of each monolayer and the interpenetration of adjacent layers can be precisely manipulated through the parameters of the electrolyte solutions. The effects of the pH and ionic strength of the immersion solutions, the total film thickness, and the PPV thermal conversion parameters on the photoluminescence and electroluminescence yields have been systematically studied. Through the ISAM process we can also deposit well-defined thicknesses of different polymers at the indium tin oxide and aluminum electrode interfaces. The interface layers are found to affect the electroluminescence efficiency.

This paper reports on work to determine the feasibility of fabricating a liquid crystal display (LCD) backlight using an array of LEDs. The purpose of this backlight is to overcome the efficiency loss of the absorptive color filters in the LCD. Two types of arrays were fabricated and tested. An array of white LEDs was designed for use with an interference color separation filter. An array of red, green, and blue LEDs was designed for use with a cylindrical lenslet array which focuses the three colors onto the appropriate color apertures of the LCD. Although promising results were achieved with standard off-the-shelf LEDs, significant improvements in surface radiance uniformity and efficiency could be obtained with special beam-shaping lenses on the LEDs.

We have developed and demonstrated a reflection-mode optical fiber-based instrument for in situ monitoring and feedback control of thin film dielectric deposition processes. The instrument operates in single-wavelength or multi-wavelength mode. One end of the fiber is placed in the deposition zone, close to the samples being coated. Single or multi-wavelength light is sent down the fiber and the reflected light from the end being coated is analyzed for intensity vs. wavelength. The fiber end being coated features an easily replaced tip to prevent loss of resolution when the coating becomes too thick. For processes in which the index of refraction or composition of the thin films is fixed, the less expensive single wavelength instrument is sufficient and measures thickness of the films by counting interference fringes. For processes in which film composition or index of refraction are variable, we use a white light source and compact spectrograph to measure reflectance vs. wavelength. For critical applications like diode laser facet coating where yield loss is significant cost driver, this monitor measures the thickness and index of refraction of single and multi-layer thin films as they are deposited. More importantly, it measures the critical parameter of interest: reflectance at the actual laser emission wavelength. This instrument replaces quartz crystal oscillators and other, more complex instruments.

The reliable n⁺-ZnSSe metal-semiconductor-metal (MSM) blue-green light emitting diodes (LEDs) have been fabricated. The contact metal was CuGe/Pt/Au. The current transport mechanism agree very well with the back-to-back tunneling diodes. The kink phenomena were observed in the MSM current- voltage curves. In the metal-semiconductor interface, the element Zn in ZnSSe can be replaced by Cu results in some acceptor levels as radiative recombination centers in the MS interface. The peak wavelength in the LED electroluminescent (EL) spectra was strongly dependent on the injection currents from 5 to 40 mA. The peak wavelength and full width at half maximum are 510 and 10 nm, respectively, at 10 mA injection current. When the injection current increases to 15 mA, the peak wavelength shifted to 530 nm due to different recombination centers. Further increasing the injection currents, the peak wavelength shifted slightly to the long wavelength side.

We have found that the electrical and optical properties of GaN epilayers strongly depend on buffer TMGa flow rates and NH₃ flow rates. At low flow rate of 4 sccm, the buffer layer quality was good so the concentrations of undoped GaN epilayers decreased and a stronger band-edge emission of 362 nm can be observed in photoluminescence spectra. The carrier density of the films can be reduced from 10¹⁸ to 10¹⁷ cm^-3 by increasing the NH₃ flow rate from 0.5 up to 1 SLM and comparatively increased the near-band-edge emission. So, with a NH₃ flow rate as high as 1 SLM, the GaN epilayers with good optical quality can be obtained. The excitation power density of He-Cd laser influences the photoluminescence property of GaN epilayers. At high excitation power density of 637 W/cm², the near-band-edge luminescence (362 nm) is dominant and the deep level luminescence (near 550 nm) appears very weak. But at low excitation power density, the luminescence from defect yellow band levels is stronger than the near-band-edge transitions.

This research attempted to use metals with lower work functions, such as Ti, Al, to form ohmic contacts to n-GaN. Then we used metals with higher work functions, such as Ni, Pd, Pt, and Au to form ohmic contacts to p-GaN. The work functions of these metals indeed influence the performance of ohmic contacts, indicating that the Fermi level of GaN is unpinned. The specific contact resistance measured and calculated by TCL model, was 2.35 X 10^-3 (Omega) cm² for as-deposited Ti/Al on GaN. After RTA processes at different temperatures in the range of 400 to approximately 900 degrees Celsius, the minimum (rho) _c of 7.4 X 10^-5 (Omega) cm² can be obtained for RTA temperature of 600 degrees Celsius. The oxidized Ni/Au contact exhibited the lowest contact resistance of 1.02 X 10^-2 (Omega) cm², among Ni/Au, Pd/Au, Pt/Au contact schemes on p-GaN. It was also observed that the I-V curves of the triple-layer contact, Pt/Ni/Au, was near-linear while the others were rectifying even after annealing.

A series of Fe_(1-x)Co_xSi₂ thin films with variation of x was prepared by reactive deposition epitaxy (RDE) method. The optical properties of the samples are reported in this paper. The dielectric function of the samples was measured by spectroscopic ellipsometer in the photon energy range of 0.26 - 4.8 eV at room temperature. It's interesting to find that the dielectric function of Fe_{(1- x})Co_xSi₂ films is strongly dependent on the phase of the films: (1) The dielectric function spectra show interference peaks in the low photon energy range for the beta phase Fe_(1-x)Co_xSi₂ samples. (2) The dielectric function spectra show a feature between the semiconductor and metal feature for the samples containing both beta and sigma phase Fe_(1-x)Co_xSi₂. (3) The dielectric function spectra show metal feature for the sigma phase Fe_(1-x)Co_xSi₂ samples. According to the x-ray diffraction results, the variation of the dielectric spectra is arisen form the change of the Fe-Si phase in the samples, rather than that from the variation of x.

During the past few years several manufacturers have introduced white Light Emitting Diodes (LEDs). At the present time these LEDs do not provide sufficient luminous flux for general lighting applications. Many manufacturers are studying the possibility of grouping several LEDs and overdriving them to produce more luminous flux. The impact of higher drive current on long-term performance of LEDs is not well known within the lighting community. Therefore, an experimental study was conducted to investigate the photometric characteristics of white LEDs as a function of time for different drive currents. The LEDs investigated in this study were the 5-millimeter type that uses GaN-based blue LEDs and Y₃Al₅O₁₂ (yttrium aluminum garnet) phosphors (YAG phosphors). These LEDs produced 65 percent more light output at 55 mA compared to the light output at 20 mA. Groups of ten LEDs were driven continuously at constant current 20, 30, 50, 70, 90, and 110 mA and their relative light output were monitored at regular intervals for over 4000 hours. The light output degradation rate increased with increasing drive currents. Typically, LED manufacturers do not recommend driving these LEDs above 20 mA. However, it was noticed that the light output of these LEDs degraded to 65% of its initial value around 4000 hours even for those LEDs driven at 20 mA, which is the manufacturer recommended value for drive current. Considering the amount of flux produced by these 5 mm type white LEDs and their light output degradation rate, they are not yet suitable for general lighting applications.

In order to come up with high volume SMD-LED production encompassing 1.9 billion devices for current fiscal year we did basic exploratory work to establish structure-processing- property relations for robust epoxy casting resin packages with identical ppm level of one. Bisphenol A-based epoxy casting resins (DGEBA) with acidic ester modified Hexahydrophthalic anhydride (HHPA) hardeners using strictly controlled high-grade raw materials were formulated and thermally transferred to highly transparent polyester networks. For 1 mm thick samples transparency in the 400 to 800 nm region is above 90%. Thermal aging tests for 6 weeks at 120 degrees Celsius reveal only slight discoloration with a color distance of 2. To avoid significant light losses within the LED operating life of 100,000 hrs stress on mechanically sensitive light-emitting chips was reduced by matching glass transition temperature Tg and E-modulus to 115 degrees Celsius and 2,800 MPa, respectively. Total chloride content below 1,000 ppm imply low corrosion potential. Further, resin composition, epoxy-hardener mixing ratio as well as curing profile were adapted to materialize fast curing for demand quantities while introducing effective low stress moieties in the final structure. Low internal stress, superior thermal shock and crack resistance were derived from supreme fracture toughness: K_IC and G_IC values were 1.350 MPam^1/2 and 560 J/m². With favorable water absorption behavior LED-packages withstand all soldering processes including TTW (through the wave) soldering. Thus, SMD-LEDs fulfill electronic industry standard JEDEC LEVEL 2.

We report on the realization of red micro cavity LED's on germanium substrates, offering a significant cost advantage compared to GaAs wafers. The MCLED structure, grown by LP- MOVPE, consists of 3 GaInP quantum wells within a (detuned) 1- (lambda) AlGaInP cavity, enclosed by Al₉₅GaAs/Al₅₅GaAs DBR's, with a current spreading layer on top. MCLED's with a 200 micrometer aperture, exhibit a quantum efficiency up to 4.35% (at 10 mA) and an optical power higher than 4 mW (at 80 mA), without any packaging. The optical spectrum was centered at 650 nm, with a FWHM of plus or minus 13 nm. Because of the detuning the opening angle of these structures was as much as 120 degrees. Rudimentary packaging resulted in a luminous intensity of 2.5 cd at 30 mA, with an opening angle of plus or minus 13 degrees. Initially the electrical performance was not optimal, but additional tests and a new processing have indicated that forward biases as low as 2.0 V (at 20 mA) can be obtained for LED's on Ge-substrates. The new processing further resulted in an improved optical output with 5 mW at 80 mA. We feel there is room for further improvement, but already we have demonstrated the feasibility of germanium substrates for commercial red (to orange/yellow) LED applications.