Chapter 5 - Semiconductor Photoemissive Structures for Far Infrared Detection

Abstract

In the internal photo effect, the excited carriers, either from a metal or a metallic semiconductor, will is be emitted into an adjacent semiconductor or a dielectric, but still remaining inside the material, which can that leads to photoconductivity. This chapter focuses on internal photoemission and its uses in infrared (IR) detection. It illustrates various types of infrared detection techniques using internal photoemission detectors such as Schottky barrier IR detectors and heterojunction internal photoemission (HIP) detectors. Almost all of the internal photoemission detectors have some connection to the Schottky barrier diode ideas. The metal or the silicide electrode in the Schottky barrier diode can be replaced by GeXSi1-X epi layers to obtain HIP detectors. HIP structures have higher quantum efficiencies than the silicide detectors due to the smaller Fermi energy values giving a wider angle for the escape cone in photoemission. However, the chapter emphasizes that the absorption coefficient for SiGe will be less than that of the silicide or metal due to the lower free carrier density. The basic structure of homojunction internal photoemission detectors consists of a heavily doped layer, which acts as the IR absorber region, and an intrinsic layer, across which most of the external bias is dropped. According to the doping concentration level in the heavily doped layer, the homojunction internal photoemission detectors can be divided into three types such as homojunction interfacial workfunction internal photoemission (HIWIP) type I having Na (doping concentration) < Nc (Mott transition value), type II having Nc < Na < N0(critical concentration), and type III having Na > N0. The chapter describes all three types in detail, focusing on their properties. It closes with a discussion on pixelless far infrared (FIR) imager.