This paper reviews those characterization techniques that have played significant roles in the development of HaCdTe infrared detector technology. We focus on the two specific HgCdTe devices that have achieved widespread application for infrared detection in the LWlR (8-12 um) and VLWlR (12-20 pm) spectral regions: the simple n-type photoconductor and the P-on-n LPE heterojunction photodiode. We review the device physics of these two detectors, relate device performance to starting material properties and processing parameters: and describe the most imoortant characterization techniques that have had a role in their development.
This paper reports data for back-illuminated planar n-on-p HgCdTe electroninitiated avalanche photodiode (e-APD) 4 · 4 arrays with large unit cells (250 · 250 lm 2 ). The arrays were fabricated from p-type HgCdTe films grown by liquid phase epitaxy (LPE) on CdZnTe substrates. The arrays were bumpmounted to fanout boards and characterized in the back-illuminated mode. Gain increased exponentially with reverse bias voltage, and the gain versus bias curves were quite uniform from element to element. The maximum gain measured was 648 at -11.7 V for a cutoff wavelength of 4.06 lm at 160 K. For the same reverse-bias voltage, the gains measured at 160 K for elements with two different cutoff wavelengths (3.54 lm and 4.06 lm at 160 K) show an exponential increase with increasing cutoff wavelength, in agreement with BeckÕs empirical model for gain versus voltage and cutoff wavelength in HgCdTe e-APDs. Spot scan data show that both the V = 0 response and the gain at V = -5.0 V are spatially uniform over the large junction area. To the best of our knowledge, these are the first spot scan data for avalanche gain ever reported for HgCdTe e-APDs. Capacitance versus voltage data are consistent with an ideal abrupt junction having a donor concentration equal to the indium concentration in the LPE film.
We report the implementation of recent advances in metalorganic chemical vapor deposition (MOCVD) for in situ growth of four-layer HgCdTe mid wave/ long wave (MW/LW) simultaneous dual-band 64 • 64 infrared detector arrays. This independently accessed, simultaneous, double-heterojunction p-n-N-P dualband detector has two back-to-back stacked photodiodes grown on CdZnTe (100) substrates. The LW photodiode is a p-on-n heterojunction grown on top of an MW N-on-P heterojunction photodiode. Secondary ion mass spectrometry depth profiles of these 28 pm thick p-n-N-P dual-band films show four well-defined regions of alloy composition and doping, and agree well with the device design. 64 x 64 arrays of dual-band detectors were fabricated from these films using electron cyclotron resonance dry etching and CdTe passivation, and hybridized to a dual-band readout chip. Two bump inter-connects in each unit cell provide independent electrical access to the back-to-back MW and LW photodiodes, and allow the MW and LW photocurrents to be separate and independent. The dualband infrared focal plane arrays (IRFPAs) spectral response data at 78K are well-behaved and are fully consistent with that observed in individual singleband LW p-on-n and MW N-on-P heterojunction devices of the same design. The hybridized 64 x 64 dual-band FPAs have MW and LW average in-band quantum efficiencies of 79 and 67%, and median D* values of 4.8 z 1011 and 7.1 x 10 l~ cm-~/Hz/W, in the respective spectral bands at 78K. The data demonstrate that MOCVD has progressed significantly toward being a practical and viable vapor phase in situ growth technology for advanced bandgap-engineered HgCdTe detector arrays.
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