This paper reports the development of 2000×256 format SWIR HgCdTe/Si FPA with multiple-choice gain (i.e. multiple-choice charge handling capacity) for hyperspectral detection. The spectral resolution is about 8nm. To meet the demands of variable low flux detection within each spectral band in the short wave infrared range, low dark current, low noise, variable conversion gains and high SNR (Signal to Noise Ratio) of FPA are needed. In this paper, we fabricate 512×512 pixel 30μm pitch SWIR HgCdTe diode array on Si by using a novel stress-release construction of HgCdTe chip on Si. Moreover, we design low noise, variable conversion gain and large dynamic range read-out integrated circuit (ROIC) and hybridized the ROIC on the HgCdTe diode array on Si substrate. There are 8-choice gains which can be selected locally according to the incident flux to meet high SNR detection demand. By high-accuracy splicing 4 512×512 HgCdTe/Si FPA we get mosaic 2000×512 FPA, and characterizations have been carried out and reveal that the array dark current densities on an order of 10-10A/cm2, quantum efficiency exceeding 70%, and the operability of 99.5% at operating temperature of around 110K. The SNR of this FPA achieved 120 when illuminated under 5×104photons/pixel.
The weakness of HgCdTe materials is a weak Hg–Te bond, which results in bulk, surface and interface instabilities.
Usual surface preparation methods for bulk HgCdTe wafers are chemical etch with bromine-in-methanol (Br-MeOH).
Because the bromine etch forms Te-enrich HgCdTe surface due to the depletion of Hg and Cd. This Te-enrich surface
layer is easily oxidized when exposed to air or acids, and this native oxide is one of the main reasons degrading the
passivation properties. Besides the surface of the material will have more damages during the ion implantation, which is
used to process a junction. In this way, appropriate surface passivation is required and is very important for HgCdTe
photovoltaic detectors. This paper presents the different surface treatment methods on the I-V characteristics of HgCdTe
infrared photovoltaic detectors. The results of the experiments show that the performance of the diodes with surface
treatment by the bromine-in-ethanol etching and lactic acid in glycol solution oxidation is better than other diodes, which
have no surface treatment or only bromine-in-ethanol etching. So it proves that the process of surface treatment in
appropriate methods can improve the quality of surface passivation.
Deposition in thermal ambience can obtain better CdTe passivation layers compared with general evaporation process. HgCdTe infrared focal plane arrays are fabricated to confirm the new process works well. Contrast n+-on-p planar photodiodes are manufactured from the same HgCdTe epilayer. Some use new process while others use general process. The performance of devices using new process shows a significant improvement. The device with general passivation process has a dark current of 7.8×10-7 A at 50 mV negative bias voltage, and the differential resistance at zero bias is 2.6×105 Ω. Meanwhile, the device with new passivation process has a dark current of
1.7×10-8 A at 50 mV negative bias voltage, and the differential resistance at zero bias is 8.0×105 Ω. Moreover, this new heating process provides a better thermal stability. The performance of devices with general passivation process declines after a long time baking at 70 °C. But the performance of the devices with heating passivation process improves a little after a long time baking even at 80 °C. The results show that CdTe deposition by vacuum evaporation in a thermal ambience can make a good HgCdTe surface passivation protection.
This paper aims to analysis the characteristics of VLWIR HgCdTe detectors with n-on-p implanted planar junction. We
use the variable area test structures, which are used as an important tool to access the quality of the material, process and
surface passivation in HgCdTe device technology. Through analyzing the relation between the inverse of the zero-bias
resistance-area product of a diode and its perimeter-to-area ratio, we can distinguish the contributions of bulk and surface
effects, and calculate the minority carrier diffusion length, which can reflect the conditions of the HgCdTe epitaxy.
According to the results, we find the VLWIR HgCdTe detectors have abnormal current-voltage phenomenon at a low
temperature, which may be the results of a parasite p-n junction. Besides, through data analysis and curves fitting, we
find the surface current of the VLWIR HgCdTe diodes at 80K is nearly comparable with the bulk current.
This paper presents the recent progress on the study of device processings at multilayer HgCdTe film for integrated two-color (SWIR/MWIR) n-p-P-P-N detector arrays. The four-layer p-P-P-N heterostructures Hg1-xCdxTe film needed to achieve two color detector arrays was grown by molecular beam epitaxy (MBE) on (211)B oriented GaAs substrates. The secondary ion mass spectroscopy (SIMS) data for the HgCdTe film was obtained. The p-type layer on top of a thin P-type potential barrier layer and the SWIR P-on-N homojunction photodiode formed in-situ during MBE growth using indium impurity doping was processed into the MWIR planar photodiode by selective B+-implantation. The preliminary 256×1 linear arrays of SWIR/MWIR HgCdTe two-color FPAs detector were then achieved by mesa isolation, side-wall passivation and contact metallization. At 78K, the average R0A values of SWIR and MWIR are 3.852×105 Wcm2 and 3.015×102 Wcm2, and the average peak detectivities Dλp* are 1.57×1011cmHz1/2/W and 5.63×1010 cmHz1/2/W respectively. The SWIR photodiode cut-off wavelength is 3.04μm and the MWIR photodiode cut-off wavelength is 5.74μm, quite consistent with the initial device design. The SWIR response spectrum of the two-color detector with a distinct fall-off at shorter wavelength regime was discussed especially.