High Performance Very Long Wavelength Multiple Quantum Well Infrared Hot Electron Transistors

Very long wavelength infrared photodetectors covering the spectral range from 14 μm to 20 μm are of great interest for a variety of space applications, and global atmospheric monitoring. The very long wavelength infrared hot-electron transistor (VWIHET) consists of a QWIP, followed by a base, and an energy filter at the collector. The details involved in the modeling, design and characterization of the VWIHET are described in this thesis. This work shows that the III-V multiple quantum well VWIHET demonstrates performance that is unrivaled by its competitor technologies. This includes high detectivity at high temperatures, low dark current, low noise currents, high uniformity among detectors in an array, as well as high output impedance for read -out circuit coupling. First, detailed modeling of the optical properties of the basic multiple quantum well infrared photodetector (QWIP) is presented. The absorption strength, peak position and lineshape are well predicted, and are widely tunable over a variety of wavelengths. Second, the origin of the leakage dark current at different temperatures is determined by studying the activation energy characteristics of the QWIP and VWIHET. The study also confirms that the filter can reduce a component of the QWIP leakage dark current and therefore increase the detector impedance and detectivity. Next, the electron transport properties of a VWIHET are studied in detail using hot electron spectroscopy. The observed photocurrent and dark current electron distributions mapped at different temperatures and biases show that the electrons execute diffusive transport across the QWIP, and that their respective initial energies are solely determined by their excitation source. A simple calculation of the VWIHET performance is presented and compared to experimental results. On the basis of the experimental results, two VWIHETs are designed for high sensitivity, background limited performance at mid-to-high temperatures. Overall, the filter structure is shown to increase the detectivity, increase the detector impedance to reduce the readout noise, reduce the current level for high temperature operation, provide cutoff wavelength and peak wavelength selection, reduce the generation-recombination noise and 1/f noise of a QWIP and increase the yield and relaxes the material quality requirements.