Engineering topics
Publications and source records attributed to Gunapala, S. D..
The performance of GaAs/AlGaAs quantum well infrared photodetectors (QWIP) specified in terms of background limited temperature T*** and specific detectivity D* has been calculated based on realistic detector parameters.
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We demonstrate the first longest-wavelength quantum-well infrared photodetector using non lattice-matched In_xGa_(1-x)As/GaAs materials system. The detectivity has been found to be comparable to those achieved with the usual lattice-matched GaAs/Al_xGa_(1-x)As detectors.
We have demonstrated a bound to continuum state GaAs/Al_xGa_(1-x)As infrared hot electron transistor which has a peak response at theta_p = 16.3 micrometers. An excellent photo-current transfer ratio of alpha_p = 0.12 and very low dark current transfer ratio of alpha_d = 7.2x10^(-5) is achieved at a temperature of T = 60 K.
Utilizing the low temperature silicon molecular beam epitaxy (MBE) growth of degenerately doped SiGe layers on Si, long wavelength stacked SiGe/Si heterojunction internal photoemission (HIP) infrared detectors with multiple SiGe/Se layers have been fabricated and demonstrated.
A photoresponse model has been developed for the Si_(1-x)Ge_x/Si heterojunction internalphotoemission (HIP) infrared detector at wavelengths corresponding to photon energies less than theFermi energy. A Si_(0.7)Ge_(0.3)/Si HIP detector with a cutoff wavelength of 23 micrometers andan emission coefficient of 0.4 eV^(-1) has been demonstrated. The model agrees with the measureddetector response at lambda greater than 8 micrometers. The potential barrier determined by themodel is in close agreement (difference similar to 4 meV) with the potential barrier determined by theRichardson plot, compared to the discrepancies of 20-50 meV usually observed for PtSi Schottkydetectors.
We demonstrate the first long-wavelength (=20) quantum well infrared photodetector using non-lattice matched InGaAs/GaAs materials system. High optical gains (low capture probabilities) were achieved by using GaAs as a barrier material in this system.
We have demonstrated the first very long wavelength (16 micrometers) infrared hot electron transistor (IHET). This device utilizes a bound to continuum GaAs/A1_xGa_(1- x)As (X=0.11) quantum well infrared photodetector (QWIP) as a photosensitive emitter, a wide quantum well as a base, and a thick A1_xGa_(1-x)As (X=0.11) barrier between the base and the collector as an energy discriminating filter. This energy filter blocks the lower energy electrons, which drain through the base while higher energy photo electrons pass to the collector. Therefore, the detectivity of the device at the collector is much higher than the detectivity at the emitter.
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-quasi-continuum, 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.