S. D. Gunapala

Photoexcited escape probability, optical gain, and noise in quantum well infrared photodetectors

We present a detailed and thorough study of a wide variety of quantum well infrared photodetectors (QWIPs), which were chosen to have large differences in their optical and transport properties. Both n‐ and p‐doped QWIPs, as well as intersubband transitions based on photoexcitation from bound‐to‐bound, bound‐to‐quasicontinuum, and bound‐to‐continuum quantum well states were investigated. The measurements and theoretical analysis included optical absorption, responsivity, dark current, current noise, optical gain, hot carrier mean free path, net quantum efficiency, quantum well escape probability, quantum well escape time, as well as detectivity. These results allow a better understanding of the optical and transport physics and thus a better optimization of the QWIP performance.

Normal incidence hole intersubband absorption long wavelength GaAs/AlxGa1−xAs quantum well infrared photodetectors

The first long wavelength quantum well infrared photodetector based on valence band intersubband absorption holes is demonstrated. A normal incidence quantum efficiency of η=28% and detectivity of D*λ=3.1×1010 cm √Hz/W at T=77 K, for a cutoff wavelength λc=7.9 μm, have been achieved.

InGaAs/InP long wavelength quantum well infrared photodetectors

We demonstrate the first long‐wavelength quantum well infrared detector using the lattice‐matched In0.53Ga0.47As/InP materials system. The responsivity has been found to be larger than that for similar GaAs/AlxGa1−xAs detectors.

Lattice-matched InGaAsP/InP long-wavelength quantum well infrared photodetectors

We demonstrate the first long‐wavelength quantum well infrared photodetector using the lattice‐matched n‐doped InGaAsP/InP materials system. A 45° prism coupled illumination responsivity of R=0.3 A/W and detectivity of D*λ=1.3×109 cm√Hz/W at T=50 K, for a cutoff wavelength λc=13.2 μm have been achieved.

Photovoltaic GaAs quantum well infrared detectors at 4.2 μm using indirect AlxGa1−x barriers

We have demonstrated the first bound to continuum state GaAs/AlxGa1−xAs quantum well infrared detector which has a peak response λp=4.2 μm in the center of the midwavelength (λ=3–5 μm) infrared band. Although the detector uses indirect AlxGa1−xAs barriers, excellent hot‐electron transport and a high detectivity D*λ=1012 cm√Hz/W were achieved.

InGaAs/InP hole intersubband normal incidence quantum well infrared photodetector

We demonstrate the first In0.53Ga0.47As/InP p‐doped quantum well infrared photodetector (QWIP). This detector has the shortest wavelength response, λp=2.7 μm, ever achieved in a QWIP and operates at normal incidence.

Design and performance of very long‐wavelength GaAs/AlxGa1−xAs quantum‐well infrared photodetectors

We present an extensive and detailed study of very long wavelength quantum well infrared photodetectors covering the spectral region between 14 and 20 μm. Measurements were made on seven different molecular beam epitaxy grown samples having different well widths and barrier heights. In this study we combine experimental results with theoretical analysis and focus on the relationship between the quantum well structure and detector performance, i.e., responsivity, dark current, dynamic resistance, noise current, optical‐gain, and detectivity. These results provide the basis for further optimization, and the detector parameters needed for the design of the readout circuit for focal plane arrays.

Metalorganic molecular beam epitaxial growth of InP/GaInAs multiquantum wells for infrared photodetection

Multiquantum well structures of InP/Ga0.47In0.53As were grown by metalorganic molecular beam epitaxy for the fabrication of infrared photodetectors. The thickness and composition uniformity of the wells was determined by high‐resolution x‐ray diffraction, photoluminescence, and photoluminescence excitation experiments. The intersubband absorption spectrum of the multiquantum well structures optimized for infrared detection is found to be in the 7–8 μm range.

InP-based quantum-well infrared photodetectors

We demonstrate the first long wavelength quantum well infrared photodetectors (QWIPs) using lattice matched n-doped In0.47As/InP and n-doped 1.3 micrometers InGaAsP/InP materials systems. The responsivity of In0.52Ga0.47As/InP detectors has been found to be larger than that for similar GaAs/AlxGa1 - xAs detectors. In addition we demonstrate the first p-doped In0.53Ga0.47As/InP QWIPs. This detector has the shortest wavelength response, (lambda) p equals 2.7 micrometers , ever achieved in a QWIP and operates at normal incidence.

Long-wavelength GaAs/AlxGa1-xAs quantum-well infrared photodetectors

We discuss the physics and 128 X 128 array imaging performance of GaAs/AlxGa1-xAs n-doped quantum well infrared photodetectors (QWIPs). The device physics of novel p-doped QWIPs which respond to normal incidence radiation of also presented.