A Voltage-Tunable Two-Color InGaAs/AlGaAs Quantum Well Infrared Photodetector
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A VOLTAGE-TUNABLE TWO-COLOR InGaAs/AlGaAs QUANTUM WELL INFRARED PHOTODETECTOR Brandon Passmore1, Jie Liang1, Da Zhuang1, Omar Manasreh1,Vasyl Kunets2, and Greg Salamo2 1 Electrical Engineering and Microelectronics and Photonics, University of Arkansas, Fayetteville, AR, 72701 2 Physics, University of Arkansas, Fayetteville, AR, 72701 ABSTRACT
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A voltage-tunable two-color multiple quantum well infrared photodetector was fabricated with two bands at 6.0 and 10.3 m. The molecular beam epitaxy grown structure consists of two stacks of n-type InGaAs wells and GaAs/AlGaAs superlattice barriers. The 6.0 m band was found to be dominant at low bias voltages while the 10.3 m band is dominant at high bias voltages. The optical absorption measurements confirm the presence of both bands. Furthermore, the transfer matrix method is used to estimate the peak position energies of the intersubband transitions in the two stacks.
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INTRODUCTION Over the past two decades there has been increasing interest in developing quantum detectors based on intersubband transition due to their applications in surveillance, night vision and remote sensing (see for example [1] – [3]). As a result of the mature growth technology of GaAs using the molecular beam epitaxy (MBE) technique and the flexibility of structure designs, multi-color quantum well infrared photodetectors (QWIPs) have emerged as a viable solution for multi-spectral infrared imaging. Multi-color QWIPs not only eliminate the need for individual single color QWIPS to be packaged together but also save valuable chip space which allows a higher density of focal plan arrays. In this study, the photoresponse of a bias-controlled two-band n-type QWIP based on InGaAs multiple quantum wells is presented for defense system applications. The optical absorption technique was used to verify the presence of the two-bands that are due to the intersubband transitions. Additionally, the electrochemical capacitance-voltage (ECV) technique was utilized to determine the doping profile of the structures. A good agreement between the optical absorption and photoresponse spectra was obtained. The bound state energy levels in the quantum structure were calculated using the transfer matrix method.
EXPERIMENT The photoresponse was measured using a Bruker IFS 125HR Fourier transform infrared spectrometer. A Stanford Research System Model SR570 low-noise current preamplifier was interfaced with the spectrometer. The preamplifier was not only used to apply a bias voltage but also to amplify the output photocurrent of the device. The photoresponse for the two-color n-
type QWIP was measured at 5 K even though the photoresponse was observed at a temperature as high as 85 K. The optical absorption was measured using the same Bruker spectrometer. Due to the quantum mechanical selection rules which only allow the absorption of radiation polarized in the plane of incidence [4], the samples were polished into a 45° waveguide configuration to allow multiple passes through the quantum structure. A
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