A new cleaning process for HgCdTe was designed，which used the improved SC-1,SC-2 and Br2- C2H5OH solutions as the main cleaning fluid and applied mega sound waves in the cleaning process. By analyzing the test results carried out on the HgCdTe surface, it was found that the material of HgCdTe for the application of new cleaning process was better than the one for the application of conventional cleaning process in the minority carrier lifetime, residual organic contamination, responsivity and specific detectivity.
The ultraviolet imaging sensors consist of two important parts: the array of detectors and the read out integrated circuits. Along with the demand for the fine resolution, large input dynamic range and high integration degree of the imaging sensors, the functions of read out integrated circuits are becoming more and more important. The on chip analog to digital conversion is the main directions of research on this area. In this paper, we presented a new digital read out integrated circuits for ultraviolet imaging sensors. The proposed circuits have an analog to digital converter in each pixel, which enable the parallel analog to digital conversion of the whole pixel array. The developed circuits have a 50um×50um pixel area with a 128×128 size, and are designed in a 0.35um four metal double poly mixed signal CMOS process. The simulation results show that the designed analog to digital converter has an accuracy of 0.2mV and can achieve the dynamic range of 88dB. The proposed circuits realize the low noise and high speed digital output of read out integrated circuits for ultraviolet imaging sensors.
CdZnTe is the most suitable epitaxial substrate material of HgCdTe infrared detectors, because its lattice constant is able to achieve full match with HgCdTe’s lattice constant. It is always needed to etch CdZnTe substrate during the process of device separation or when we want to fabricate micro optical device on CdZnTe substrate. This paper adopts the more advanced method, Inductive Coupled Plasma-Reactive Ion Etching(ICP-RIE). The etching conditions of ICP-RIE on CdZnTe substrate are explored and researched. First of all, a set of comparative experiments is designed. All of CdZnTe samples with the same component are polished by chemical mechanical polishing before etching. Then all samples are etched by different types of etching gases(CH4/H2/N2/Ar) and different ratios of gases as we designed. The etching time is all set to 30 minutes. After that, the surface roughness, etching rate, etching damage and the profile of etched mesas are tested and characterized by optical microscope, step profiler and confocal laser scanning microscope (CLSM), respectively. It is found that, Ar gas plays the role of physical etching, but the etching rate will decline when the concentration of Ar gas is too high. The results also show that, the introduction of N2 causes more etching damage. Finally, combination of CH4/H2/Ar is used to etch CdZnTe substrate. The ratio of these gases is 2sccm/2sccm/10sccm. The testing results of optimized etching show that, the maximum etching rate reaches up to 20μm/h and the etched CdZnTe surface is smooth with very low etching damage. At last, aimed at the shortcoming of photoresist’s degeneration after long-time etching, the ICP etching process of CdZnTe deep mesa is studied. Double-layer or triple-layer photoresist are spin-coated on CdZnTe substrate during the process of lithography. Then ICP etching is carried out with the optimized condition. It is seen that there is no more phenomena of degeneration.
Performance of HgCdTe devices was limited by many factors such as materials and techniques, etc. And the electrical
characteristics of electrode contacts on HgCdTe played important roles．Because Ar Ion Beam Etching could make the
conductivity type conversion of p-type HgCdTe material, it was used to obtain n-type electrode area on the slight-p type
HgCdTe material. Variable magnetic field Hall measurements were performed on n-type and slight p-type HgCdTe
material before and after Ar Ion Beam Etching at 77 K. The mobility spectrum analysis (MSA) technique was employed in
this paper to obtain the electrical parameter of HgCdTe. Comparing the electrical parameters of HgCdTe before and after
etching, we knew that Ar Ion etching formed high doping concentration n-type area on slight p-type HgCdTe. The minority
carrier lifetime of HgCdTe was studied using the photoconductive decay technique. By measuring the minority carrier
lifetime of the same HgCdTe material with or without n-type electrode, it was found that the minority carrier lifetime of
slight p-type HgCdTe with n-type electrode was higher than HgCdTe that was without n-type electrode at low temperature.
The results showed that the n-type electrode could improve the minority carrier lifetime of slight p-type HgCdTe. In
addition, by changing the distance of the n-type electrode area to the photosensitive area, it was researched that the impact
of n-type electrode area on the device performance. With the decrease of distance, the device performance improved. It was
proved that n-type electrode areas also could improve the performance by device fabrication.
The semiconductor-passivating layer interface, as well as the dielectric properties of the passivants, plays an important role in HgCdTe based photoelectric detectors. Anodization is a commonly uses surface passivation for HgCdTe. ZnS is deposited on the AOF (anodic-oxide film) as antireflecting layer. The interfacial properties of the metal insulator semiconductor (MIS) structures were determined by capacitance-voltage (C-V) measurements in the frequency range 10 KHz-10 MHz. The results showed that the MIS detector could not reach the high frequency level even at frequencies up to 10 MHz. The interfacial state densities were 3.4×1011 cm-2q-1V-1 and the fixed charges were 1.1×1012 cm-2. The surface recombination velocity was 700 cm/s.