Advances in linear and area HgCdTe APD arrays for eyesafe LADAR sensors

Abstract

HgCdTe APDs and APD arrays offer unique advantages for high-performance eyesafe LADAR sensors. These include: operation at room temperature, low-excess noise, high gain, high-quantum efficiency at eyesafe wavelengths, GHz bandwidth, and high-packing density. The utility of these benefits for systems are being demonstrated for both linear and area array sensors. Raytheon has fabricated 32 element linear APD arrays utilizing liquid phase epitaxy (LPE), and packaged and integrating these arrays with low-noise amplifiers. Typical better APDs configured as 50-micron square pixels and fabricated utilizing RIE, have demonstrated high fill factors (>80%), low crosstalk (<2%), excellent uniformity, low dark currents (<10nA), and noise equivalent power (NEP) from 1 -2 nW. Two units have been delivered to NVESD, assembled with range extraction electronics, and integrated into the CELRAP laser radar system. Tests on these sensors in July and October 2000 have demonstrated excellent functionality, detection of 1-cm wires, and range imaging. Work is presently underway under DARPA's 3-D imaging Sensor Program to extend this excellent performance to area arrays. High-density arrays have been fabricated using LPE and molecular beam epitaxy (MBE). HgCdTe APD arrays have been made in 5 x 5, 10 x 10 and larger formats. Initial data shows excellent typical better APD performance with unmultiplied dark current <10 nA; and NEP <2.0 nW at a gain of 10.

Infrared Avalanche Photodiode Detectors

“…Impact ionisation process is initiated at high reverse bias in these materials. Evacuation rate of charge carriers from the depletion region is also slow [8][9][10][11][12] . High excess noise factor (F) is reported in Si and III-V based materials due to the involvement of both type of carriers (electrons and holes) in the multiplication process.…”

“…Geiger mode APD has been used to perform photon detection application in the past. However, the recent advances in low noise amplifier design and device fabrication techniques for suppressing APD multiplication noise have led to the development of a new generation of linear mode single photon counting APD (linear SPAD) [5][6][7][8] . The high dark current and long dead times limit to the Geiger mode APD based LADAR seekers for detection of the incoming signals.…”

“…The high dark current and long dead times limit to the Geiger mode APD based LADAR seekers for detection of the incoming signals. The Linear APD has been more beneficial: (i) To find the range information from more than one target in a pixel's instantaneous field of view (FOV) (ii) To detect the target behind debris with low false alarm rate (iii) Can employ thresholding technique to reject dark current when they receive reflected signals, and (iv) Enable to record the signal intensity that is beneficial to increase in the efficiency [8][9][10] . In this paper, the significant results of HgCdTe and III-V based APD detector achieved by the leading group are included.…”

“…High gain with low noise and wide bandwidth are vital for imaging applications. Avalanche photodiodes perform the functions of detection and amplification for the attenuated optical signals in the battle field and long range applications, especially in space based thermal imaging applications [1][2][3][4][5][6][7][8][9][10][11][12][13][14] . APD provides high internal gain and fast response time, which are needed to meet the system requirements.…”

Third-generation sensors for night vision

“…The first type of HgCdTe APD [9] relies on a novelty in the energy band structure of HgCdTe with a bandgap of approximately 0.82 eV. Here the bandgap energy becomes equal to the energy separation between the top of the valence band and the split-off light-hole band below it.…”