Optimization of fabrication processes of the mesa-type GaAs:Te blocked-impurity-band detector
In this work, the device structure of the mesa-type GaAs:Te blocked-impurity-band detector was designed. The fabrication processes were presented briefly, and optimization of the fabrication processes was investigated. A 3-micron-thick SiO2 film was deposited as resist to substitute for photoresist in the 50-micron-deep mesa etching process. In addition, a bi-layer photoresist lithography technique was adopted to optimize the process of electrode fabrication. It is demonstrated that the device quality can be improved significantly after optimization.
Development for Germanium Blocked Impurity Band Far-Infrared Image Sensors with Fully-Depleted Silicon-On-Insulator CMOS Readout Integrated Circuit
We are developing far-infrared (FIR) imaging sensors for low-background and high-sensitivity applications such as infrared astronomy. Previous FIR monolithic imaging sensors, such as an extrinsic germanium photo-conductor (Ge PC) with a PMOS readout integrated circuit (ROIC) hybridized by indium pixel-to-pixel interconnection, had three difficulties: (1) short cut-off wavelength (120 $$\upmu $$μm), (2) large power consumption (10 $$\upmu $$μW/pixel), and (3) large mismatch in thermal expansion between the Ge PC and the Si ROIC. In order to overcome these difficulties, we developed (1) a blocked impurity band detector fabricated by a surface- activated bond technology, whose cut-off wavelength is longer than 160 $$\upmu $$μm, (2) a fully-depleted silicon-on-insulator CMOS ROIC which works below 4 K with 1 $$\upmu $$μW/pixel operating power, and (3) a new concept, Si-supported Ge detector, which shows tolerance to thermal cycling down to 3 K. With these new techniques, we are now developing a $$32 \times 32 $$32×32 FIR imaging sensor.
Electric field and responsivity modeling for far-infrared blocked impurity band detectors
One-dimensional numerical modeling is presented for Ge:Ga far-infrared (IR) blocked impurity band (BIB) detectors in the low field, unity gain regime. Spatial variations of space charge, electric field, free carrier, and hopping currents are calculated to illustrate the effects of variations in absorbing layer compensation, blocking layer doping, and blocker/absorber interface gradient. Increased blocking layer doping and broader interface doping gradients lead to significant field variations. These field nonuniformities can increase responsivity by increasing field penetration and associated current collection in the absorbing layer. The ratio of photocurrent to dark current remains constant over a range of blocking layer doping, suggesting that extremely high purity blocking layers may not be required for far-IR BIB fabrication.