The optical properties of InGaAsN structures for the fabrication of photodetectors are investigated. An expression for the bulk bandgap as a function of the nitrogen fraction is obtained from x-ray diffraction, photoreflectance and photoluminescence measurements. Optical absorption of undoped MQW structures show that the cutoff wavelength is extended due to the presence of nitrogen. A functioning heterojunction phototransistor was fabricated. Photocurrent spectra show that a responsivity higher than 1.5 A/W is obtained with a cutoff wavelength of 1.16 micrometers . I-V measurements under different light levels show that a peak gain of 5 is obtained with a collector current of 260 (mu) A and a dark current lower than 2 nA with a 10V bias.
Intermixing of the well and barrier layers in quantum well infrared photodetectors (QWIPs) can be used to realize a broadened spectral response as well as multiple color detectors. We describe die experimental results of both rapid thermal annealing (RTA) and laser annealing (LA) QWIPs operating in the 8-12µm regime. The peak spectral response of the annealed detectors was shifted to longer wavelength as compared to die as-grown detectors. In general, a decrease in detector performance after annealing is also observed which may be attributable to a change in the absorption coefficient caused by the out-diffiision of dopants during annealing. Recent advances in growth technology, complimented by innovative structures should offset any degredation in performance. Thus, the post-growth control of the composition profiles by annealing offers opportunities to fine tune various aspects of a QWIP’s response.
A 2D finite difference method is employed to demonstrate the effectiveness of the use of guard rings in reducing surface electric field along the semiconductor/insulator interface of planar avalanche photodetectors (APDs). Results from our modeling indicate a 20 percent edge field reduction in doubly-diffused devices as compared to singly-diffused p+n- junctions. The introduction of guard rings and double diffusion process is shown to provide an extra degree-of-freedom in the design of APDs, thus improved device characteristics against breakdown fields.
A low-threshold second-harmonic generation horizontal cavity surface emitting laser (SHG-HCSEL) operating at 0.49 micrometers under electrical pumping is proposed and theoretical design considerations are presented. The strained InGaAs quantum well (QW) laser, implemented on a nearly optimally oriented (311)B-GaAs substrate, incorporates a reduced Al-content, quasi-phase matched (QPM) single guiding GaAs layer (SGL) structure, a novel double-tapered horizontal waveguide with high reflection-coated cleaved facets, and a metallization- free emission window at the center of the device. The horizontal geometry serves to increase the ratio of fundamental power density within the SHG-region to that at the facets, thereby increasing the laser optical power at the onset of catastrophic optical damage (COD) at the facets. Simulations indicate that surface blue emission (on the order of 14 W/cm2 peak, corresponding to 50 (mu) W for a 10 micrometers X 100 micrometers emission window) can be obtained from a compact device, with a moderate taper angle of 3 degree(s), operating well below the COD limit. The model also shows that a SGL thickness of 175 nm corresponds with the second QPM-SHG efficiency peak which coincides with peak optical confinement in the QW. Finally, AlGaAs cladding thickness of 113 nm is found to be the optimum etch condition beneath the SHG emission window.
We report normal incidence infrared electroabsorption modulation utilizing the Stark effect to induce (Gamma) -L transitions in asymmetric AlSb/InAs/Al0.4Ga0.6Sb/GaSb/AlSb quantum wells on a undoped GaSb substrate grown by molecular beam epitaxy. The normal incidence measurements of the fabricated devices were performed under various electric fields at T equals 77K using a Fourier transform infrared spectrometer. The modulation absorption was found to be directly proportional to applied bias. The largest infrared absorption at 5 micrometers with an absorption coefficient of 3200 cm-1 was obtained at 14 V reverse bias. Our results indicate the potential of this novel structure for application in normal incidence modulators.
A novel guard ring p-i-n photodiode is designed and fabricated to solve the slow-tail problem associated with typical p-i-n photodiodes. The device incorporates an additional diffused p+ region around the active layer to circumvent the problem of slower responses due to diffusion currents. The effectiveness of the guard ring in providing low Bit-Error-Rate is quantified. The Extinction Ratio of the device with a 20nsec pulse is in excess of 31 dB.
A novel approach for integration of an AlGaAs/GaAs double heterojunction bipolar transistor (D-HBT) with an InGaAs quantum well (QW) laser is demonstrated. The QW of the laser is incorporated within the lightly doped GaAs collector region of the HBT while the p+-base and n+- region of the collector are used compatibly as the electrodes of the laser diode, thus eliminating the need for an independent laser structure. Advantages of this approach include single-step molecular beam epitaxial (MBE) growth without the thermal cycling associated with sequential growth or selective regrowth techniques. In addition, elimination of wire interconnects and corresponding parasitics between the HBT collector and the laser diode enhance the performance of the HBT/laser diode circuit. HBTs with current gain as high as 60 and compatible InGaAs quantum well lasers with room temperature threshold current density as low as 500 A/cm2 have been successfully fabricated. Results demonstrate that the structure has potential for application in optoelectronic integrated circuits (OEICs), fiber optic communications, and optical interconnects.
A novel punch-through heterojunction phototransistor (PTHPT) integrated with a compatible modulation doped FET (MODFET) was fabricated. The two terminal operating PTHPT can provide the superior properties of high optical gain and high speed. This is done without introducing an amplified shot noise associated with a base bias current as found in a three terminal operating heterojunction phototransistor (HPT). The PTHPT fabricated in a 0.8-micrometers GaAs/AlGaAs material system exhibits an optical conversion gain as high as 1250 at an incident optical power as low as 0.5 (mu) W. The gain changes less than 15 percent over a 20 dB range of the incident optical power. The transient measurements show that the PTHPT has a higher response speed than that of a conventional HPT. The compatible MODFETs with 1-micrometers gate lengths exhibit transconductances over 200 ms/mm and a current density of 160mA/mm. The principle presented here can also be applied to other material systems such as GaSb/AlSb and InGaAs/InP for long wavelength optical communications.
Al0.5Ga0.5Sb/GaSb metal-semiconductor-metal (MSM) detectors have been prepared on semi-insulating InP substrates. The molecular beam epitaxially grown samples on differently orientated substrates exhibit different types of conductivity. The Schottky barrier height between Al and Al0.5Ga0.5Sb grown on (311)B oriented substrates is 0.6 eV, while the Al contacts on (100) sample exhibit ohmic behavior. The results show that the Sb- deficiency related p-type native defect density is significantly reduced in the samples grown on (311)B oriented substrates. The 3-dB device response bandwidth is about 1 GHz at room temperature and beyond 10 GHz at 77 K.
GaSh-based meta1semiconductor-meta1 (MSM) and pi-n photodetectors grown by molecular beam epitaxy have been demonstrated for the first time. These novel devices can offer higher bandwidths and lower excess noise because of the superior hole transport properties of GaSb and the enhanced hole ionization rate of A1GaSb alloys. MSM photodetectors employing GaSb active region and AlGaSb barrier enhancing abrupt region are grown on InP substrates, while p4n photodiodes are grown on GaSb substrates. These MSM detectors exhibit photoresponse in the range of 0.2-0.65 AJW and a 3 dB bandwidth exceeding 1 GHz at 300 K and 10 GHz at 77 K. The dark currents of 106 A at 300 K and 1010 A at 77 K are measured for 25 x 25 devices. The p-i-n photodiodes have breakdown voltages as high as 20 V. The leakage currents of these devices are 60 i.i.A at half the breakdown voltage and 10 pA after nitrogen plasma passivation for 40 x 40 devices. To the best of our knowledge, these are the best results obtained from the structures grown by MBE.
We have demonstrated the fabrication of two structures achieved by the thin ifim transfer technique: back4lluminated InAlAsfInGaAs metal. semiconducthr-metal (MSM) detectors with buried interdigitated fingers on GaAs substrates; and long wavelength InGaAsP lasers on GaAs or Si substrates. For optoelectromc system applications, one often considers the use of a single material system for both the optical and electronic components on the chip, because it is not complicated by lattice mismatch. Compared to epitaxial growth of latticemismatched material systems, such as GaAs on Si, the thin ifim transfer technique does not result in a substantial number of misfit dislocations which can adversely affect device performance. The results we obtained demonstrate the feasibility of the thin film transfer process and point to the potential integration of OEICs and other components fabricated from a variety of materials on a common host substrate.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.