Ge x Si 1−x infrared detectors I. Absorption in multiple quantum well and heterojunction internal photoemission structures

Abstract

We report absorption measurements on two types of long-wave infrared detector structures. Both types were grown by ultrahigh vacuum chemical vapor deposition, and were characterized by multiple analytic techniques. In both multiple quantum well (MQW) and heterojunction internal photoemission (HIP) structures, it is found that free-carrier absorption is dominant for normally incident radiation. The measured absorption is fit well by the classical expression for free-carrier absorption, with scattering times of about 10−14 s (MQW) and 5×10−15 s (HIP). The measured absorption is used to evaluate the responsivity that results when all carriers energetically able to surmount the barrier are collected. Based on this analysis, higher responsivity is predicted for HIP detectors, largely because of the greater density of initial states. The responsivity obtained in practice depends upon the photoconductive gain (MQW detectors) or the escape probability (HIP detectors). The escape probability for HIP detectors is measured in Part II.

On the theory of internal photoemission in heterojunctions

“…Experiments showed that the incoming photons are absorbed in the film via free-carrier absorption [5,8,13]. The absorption coefficient (in cm À1 unit) is given [14] a ¼…”

“…But, neither of these models was including scattering mechanisms that the carriers experienced during their motion. Another model taking into account the scattering of excited carriers was reported by Strong et al [3,8]. In this model, they followed the model which was developed for the metal(silicide)/semiconductor systems by Vickers [9] and incorporated the wavelength and doping concentration dependent absorption.…”

Study on the long wavelength SiGe/Si heterojunction internal photoemission infrared photodetectors

“…Experiments showed that the incoming photons are absorbed in the film via free-carrier absorption [5,20,21]. The external yield can then be written as [17,19] …”

Novel quantum wire infrared photodetectors

“…However, the use of intersubband optical absorption in low dimensional semiconductors has emerged as a promising technique for IR detection. In particular, quantum well infrared photodetectors (QWIP) have been the topic of significant research and development during the past decade [4][5][6], and QWIP detectors for midand long-wavelength IR have been successfully implemented [7][8][9] using primarily GaAs, InGaAs, and SiGe [10]. Due to this effort, QWIP devices have emerged as an alternative technology for the implementation of high performance focal plane array (FPA) detectors that show enhanced performance compared to bulk material detectors such as HgCdTe and InSb [1,5].…”