This five-year program focuses on the study and demonstration of a novel idea to use optical bias for multi-color detection using monolithically integrated two-terminal multi-junction photodetectors (MJPDs), which are ideal for multicolar (>2) FPAs integrated with conventioal read-out ICs. This idea is enabled by our recently proposed II-VI (MgZnCdHg)(SeTe) and III-V (InGaAl)(AsSb) semiconductor systems lattice-matched to 6.1 GaSb and InAs substrates. These semiconductor binary and alloy materials have direct bandgaps covering the entire energy spectrum from far IR (~0 eV) to UV (~3.4 eV). Such a unique material platform offers unlimited degrees of freedom for monolithically integrating many photodiodes with different bandgaps onto a single substrate without large numbers of misfit dislocations to ensure the best materials quality. This feature is not achievable by any other known lattice-matched semiconductors on any available substrates. A dual-chamber II-VI and III-V MBE system will be used to develop the integrated (MgZnCd)(SeTe) and (InGaAl)(AsSb) semiconductor material systems for the proposed device and system applications. Many state-of-the-art materials characterization tools will be used to study the structural, optical and electrical properties of the new materials. The device fabrication will be carried out in a well-equipped cleanroom at ASU. Detailed temperature dependent device characterization will be carried out in Prof. Zhang's group. Very encouraging preliminary results of the materials development have been already achieved.
This one-year project is a supplementary program to the five-year AFOSR program Optically biased monolithically integrated multicolor photodetectors, which focuses on the study and demonstration of a novel idea to use optical biasing for multi-color detection using two-terminal monolithically integrated multi-junction photodetectors (MJPDs). The basic idea is that each MJPD consists of multiple photodiodes with different bandgaps connected in series with the same polarization and with a tunnel diode with reverse polarity in between every two connected photodiodes. This project will study HgCdSe alloys, which are nearly lattice-matched to GaSb substrates and have very similar materials properties as that of HgCdTe (MCT). Their energy bandgaps cover a very broad wavelength range from near infrared to far infrared. Due to the availability of large, lattice matched GaSb substrates, this material system could be an excellent candidate to replace MCT materials for lowcost, large-area IR FPAs. The availability of many II/VI wide bandgap materials capable of detecting green to UV which are, like HgCdSe, lattice-matched to GaSb substrates, leads to monolithic integration of all these II-VI and III-V materials on a single lattice-matched substrate. Such a system will enable novel multi-color FPAs. This lattice-matched system covering UV to IR could revolutionize nextgeneration UV-IR adaptive staring cameras for imaging and sensing applications. However, this material system has not yet been studied extensively. Here we propose a pilot program to enable monolithic UV to IR lattice-matched photodetectors by studying MBE growth of HgCdSe alloys on GaSb, including structural and optical properties. In addition, we will investigate the feasibility of tunnel junctions made of tyep-III (broken-gap) heterojunctions. Army Research Laboratory will establish a base line of MBE growth process for ternary Hg1- xCdxSe with various alloy compositions on GaSb substrates. The relationship between the alloy compositions and growth conditions of Hg1-xCdxSe will be studied. A set of growth parameters for HgCdSe alloys lattice-matched to ZnTe/Si and/or GaSb with cut-off wavelengths in one of the IR bands, especially the LWIR band, will be established. RHEED will be used to monitor the MBE growth process, and high-resolution x-ray diffraction, FTIR spectroscopy and Hall measurement will provide quick feedbacks to refine the MBE growth parameters. Arizona State University will focus on the following tasks: Materials design: This task includes an extensive literature search to prepare a thorough review of materials properties of the proposed material system. Properties of interest include the lattice constants, thermal expansion coefficients, band edge energy positions, bandgaps, carrier effective masses, optical constants, and absorption coefficients at room temperature and the intended operating temperature of 77K. Structural and optical characterization: This task will use high-resolution x-ray diffraction and high-resolution TEM to study the bulk and interface properties of grown samples. Temperature dependent photoluminescence measurements and other spectroscopic measurements will be carried out to study the optical properties of the above-mentioned materials. Tunnel junction design, growth, fabrication and testing: This task includes the design of tunnel junctions using broken-gap heterostructures and their growth using MBE. Simple devices will be fabricated and tested at ASU.
|Effective start/end date||4/15/10 → 5/14/15|
- DOD-USAF-AFRL: Air Force Office of Scientific Research (AFOSR): $798,500.00