Germanium Far Infrared Blocked Impurity Band Detectors

Abstract

We report on the development of Germanium Blocked Impurity Band (BIB) photoconductors for long wavelength infrared detection in the 100 to 250.μm region. Liquid Phase Epitaxy (LPE) was used to grow the high purity blocking layer, and in some cases, the heavily doped infrared absorbing layer that comprise theses detectors. To achieve the stringent demands on purity and crystalline perfection we have developed a high purity LPE process which can be used for the growth of high purity as well as purely doped Ge epilayers. The low melting point, high purity metal, Pb, was used as a solvent. Pb has a negligible solubility <1017 cm−3 in Ge at 650°C and is isoelectronic with Ge. We have identified the residual impurities Bi, P, and Sb in the Ge epilayers and have determined that the Pb solvent is the source. Experiments are in progress to purify the Pb. The first tests of BIB structures with the purely doped absorbing layer grown on high purity substrates look very promising. The detectors exhibit extended wavelength cutoff when compared to standard Ge:Ga photoconductors (155 μm vs. 120 μm) and show the expected asymmetric current-voltage dependencies. We are currently optimizing doping and layer thickness to achieve the optimum responsivity, Noise Equivalent Power (NEP), and dark current in our devices.

Microscopy and Electrical Properties of Ge/Ge Interfaces Bonded by Surface-Activated Wafer Bonding Technology

“…15,16) However for the far-infrared region (approximately ¼ 200 m), BIB photoconductors have not been established well because a sufficiently low-background impurity content of Ge is difficult to obtain with the conventional epitaxial methods. [17][18][19][20] The room-temperature wafer bonding may be one of the best methods to fabricate a Ge BIB structure because the floating zone (FZ)-grown or the Czochralski (CZ)-grown high-purity Ge can be individually available for each layer.…”

Ion-implanted Ge:B far-infrared blocked-impurity-band detectors

“…The devices fabricated showed response down to 50 cm À1 (200 lm), however, results were not reproducible and the detectors suffered from large dark currents due to unpassivated surfaces. Preliminary results from devices fabricated with liquid phase epitaxy (LPE)-grown Ge films using Pb as a solvent were encouraging showing some extended wavelength response [15]. The purity of commercially available Pb was found to be a problem, with n-type impurities $10 15 cm À3 , identified by photothermal ionization spectroscopy to be phosphorus.…”

Influence of the Sb dopant distribution on far infrared photoconductivity in Ge:Sb blocked impurity band detectors

“…Liquid phase epitaxy was chosen for its potential as a high purity technique with the ability to grow layers 1-100 µm thick. Preliminary results were encouraging showing some extended wavelength response [13]. LPE growth takes place as the growth materials precipitate out of a low melting point solution.…”