Homojunction internal photoemission far-infrared detectors: Photoresponse performance analysis

The concept of homojunction infernal photoemission far-infrared (FIR) detectors has been successfully demonstrated using forward biased Si p-i-n diodes at 4.2 K. The basic structure consists of a heavily doped IR absorber layer and an intrinsic (or lightly doped) layer. An interfacial workfunction between these regions defines the long-wavelength cutoff (X,) of the detector. Three types of detectors are distinguished according to the emitter layer doping concentration level. Our model shows that high performance Si FIR detectors (>40 pm) can be realized using the type-II structures with a tailorable X,, in which the absorber/emitter layer is doped to a level somewhat above the metal-insulator transition value. Analytic expressions are used to obtain the workfunction versus doping concentration, and to describe the carrier photoemission processes. The photoexcitation due to free-carrier absorption, emission to the interfacial barrier, hot-carrier transport, and barrier collection due to the image force effect, are considered in calculating the spectral response and quantum efficiency as functions of device parameters for Si n+ ’ -1 structures, leading to a detailed photoresponse analysis of type-II detectors. These results are useful for the design and optimization of type-II detectors.