Development of low dark current SiGe-detector arrays for visible-NIR imaging sensor

Abstract

SiGe based Focal Plane Arrays offer a low cost alternative for developing visible-NIR focal plane arrays that will cover the spectral band from 0.4 to 1.6 microns. The attractive features of SiGe based IRFPA's will take advantage of Silicon based technology, that promises small feature size, low dark current and compatibility with the low power silicon CMOS circuits for signal processing. This paper discusses performance comparison for the SiGe based VIS-NIR Sensor with performance characteristics of InGaAs, InSb, and HgCdTe based IRFPA's.Various approaches including device designs are discussed for reducing the dark current in SiGe detector arrays; these include Superlattice, Quantum dot and Buried junction designs that have the potential of reducing the dark current by several orders of magnitude. The paper also discusses approaches to reduce the leakage current for small detector size and fabrication techniques. In addition several innovative approaches that have the potential of increasing the spectral response to 1.8 microns and beyond. TECHNICAL DISCUSSIONThere is significant interest in developing low cost IR Sensors for a variety of applications such as low cost thermal imagers and the ability to detect and defeat incoming threats. There are several other technologies such as InGaAs, InSb and HgCdTe, which cover different part of the IR Spectrum. HgCdTe IR focal plane arrays are being developed for 3-5 and 8-14 micron applications [1]. InSb is being used for 3-5 micron applications [2].

Advances in Infrared Detector Array Technology

“…Some of the earlier attempts in developing SiGe IR detectors focused on their LWIR applicationsby using internal photoemmision [52][53]. Renewed efforts are now developing these detectors for application in the NIR-SWIR band [54]. For the SiGe material to respond to the SWIR band, its cutoff wavelength is tuned by adjusting the SiGe alloy composition.…”

“…Beyond the critical thickness, the strain is relaxed through the formation of misfit dislocations, which can cause an increase in the dark current. Several approaches have been proposed to reduce the dark current in SiGe detector arrays by several orders of magnitude.These include fabrication methodologies, de-vice size and novel device architectures, such as Superlattice, Quantum dot and Buried junction designs [54]. Furthermore, some of these approaches have the potential of extending the wavelength of operation beyond 1.8-2.0 microns.…”

“…Schematic of detector array structure consisting of a SiGe /Si strained layer Superlattice grown on (001) silicon[54].…”

SiGe Based Visible-NIR Photodetector Technology for Optoelectronic Applications

“…Group III-V compound semiconductors possess the advantages of high absorption efficiency, high carrier drift velocity, excellent noise characteristics, and mature design and fabrication technology for optical devices, and are commonly used in IR detection related devices [1]. InGaAs based IR photodetectors have been developed for NIR (up to ~1700 nm) applications, InSb for 3-5 µm applications, and HgCdTe for 1-3, 3-5 and 8-14 µm applications [2]; the spectral responses of these and various other IR detector material systems are shown in Figure 1. While it is possible to integrate III-V semiconductor materials on Si by wafer bonding or epitaxy [3], III-V based detectors normally require cooling (typically down to 77 K), and incorporating III-V materials into the prevalent silicon process is at the expense of high cost and increased complexity.…”

“…(a) I-V characteristics for 10×10 µm2 SiGe pin detector devices with and without 400°C post-metallization anneal in N 2 ; at-1 V, the dark current is reduced by ~1000X with 400°C by the annealing[24]. (b) Schematic showing composition of a prospective SiGe pin photodetector device after fabrication.…”