Vladimir V. Vasilyev

Focal plane arrays based on HgCdTe epitaxial layers MBE-grown on GaAs substrates

Heterostructures HgCdTe/CdTe/GaAs grown by molecular beam epitaxy were used for LWIR FPA fabrication. The technology was developed and 32 by 32 and 128 by 128 photodiode arrays with indium bumps of 15 micrometer height in each pixel were fabricated. Mean NEP is 1.7 by 10-13 W/Hz1/2 and 1.1 by 10-14 W/Hz1/2 for 128 by 128 photodiode arrays with (lambda) c value of 10.4 micrometer and 5.2 micrometer correspondently. The technology of hybrid assembling with continuous control of cold welding on the measuring stand was demonstrated on the example of 32 by 32 LWIR FPA. Mean NEP value of 5.4 by 10-14 W/Hz1/2 with (lambda) c equals 10.6 micrometer at 80 K operation were obtained. using an infrared camera system the infrared image was successfully demonstrated. The NETD value of 0.077 K was obtained under 293 K background condition.

HgCdTe Heterostructures on Si (310) Substrates for Midinfrared Focal Plane Arrays

Results of studies of the molecular beam epitaxial growth of HgCdTe alloys on Si substrates as large as 100 mm in diameter are presented. Optimum conditions for obtaining HgCdTe/Si(310) heterostructures of the device quality for the spectral range of 3–5 μm are determined. The results of measurements and discussion of photoelectric parameters of an infrared photodetector of a format of 320 × 256 elements with a step of 30 μm based on a hybrid assembly of a matrix photosensitive cell with a Si multiplexer are presented. A high stability of photodetector parameters to thermocycling from room temperature to liquid-nitrogen temperature is shown.

Electrical activation of boron implanted in p-HgCdTe (x = 0.22) by low-temperature annealing under an anodic oxide

Abstract The low-temperature electrical activation of boron atoms implanted in p-HgCdTe has been observed for the first time. The bulk crystals of p-Hg 0.75 Cd 0.22 Te were implanted at room temperature and at 250 °C with 150 keV B + ions up to a dose of 3 × 10 16 cm −2 through an anodic oxide with a thickness of 90 nm. The same control samples were implanted with N + ions under analogous conditions. The two-step post-implant annealing was carried out at 250 °C for 2–4 h and then at 200 °C up to 44 h in a nitrogen atmosphere. Differential Hall effect measurements at 77 K, optical reflection and secondary ion mass spectroscopy were used for implanted surface layer studies. It was established that the doping efficiency of boron atoms amounts of 0.03–14% decreasing with the increasing boron ion dose and becoming higher in the case of ion implantation at 250 °C. Mercury loss was found not to occur from the surface of HgCdTe through an anodic oxide cap during such heat treatment.

320×256 HgCdTe IR FPA with a built-in shortwave cut-off filter

A photovoltaic detector design based on the graded band gap HgCdTe MBE structure with high conductivity layer (HCL) at interface, which provides photodiodes series resistance and a shortwave cut.off filter is developed. The optimal HCL parameters giving high quantum efficiency and minimal noise equivalent temperature difference were determined by calculations and experimentally confirmed. The hybrid 320×256 IR FPA operating in 8–12 μm spectral range was fabricated. The threshold power responsivity and minimal noise equivalent temperature difference values at wavelength maximum were 1.02×10−7 W/cm2, 4.1×108 V/W and 27 mK, respectively.

IR photodetectors based on MBE-grown MCT layers

A complete technological cycle has been designed to produce photodetector arrays, which involves MBE growth of Hg1-xCdxTe (MCT) heteroepitaxial layers, fabrication of MCT-based photodetector structures, manufacture of silicon array multiplexers and hybrid assembly of a photodetector module consisting of a photodetector and multiplexer by means of indium micro bumps. Photoelectric parameters are given of photodetector array modules on the basis of photodiodes for the middle (3 - 3.5 μm) and far (8 - 12 μm) infrared ranges, operating at 78 - 80 K and 200 - 220 K temperatures.

MCT heterostructure design and growth by MBE for IR devices

The molecular beam epitaxy (MBE) set-up with analytical control equipment of growth process was designed and fabricated for growing A2B6 compounds including the mercury-containing ones. A technology was elaborated for growing mercury-cadmium-telluride (MCT) solid solution heteroepitaxial structures (HS) by molecular beam epitaxy (MBE) method with a given variation of MCT composition throughout the thickness. HSs MCT MBE on CdZnTe/GaAs substrate with different variation composition in layers at MCT film interfaces were designing and growing. These structures were used for manufacture of high quality single, linear and array photoconductors (PC) and photodiodes (PD) operating at 77 K and 200 - 250 K temperature in the wavelength range of 3 - 5 micrometer and 8 - 12 micrometer, up and over 20 micrometer. Widegap layers at MCT film interfaces are used as passivating coating. Narrowgap layer at MCT film/CdZnTe buffer layers interface is used for decrease of PD series resistance. For decrease of dark currents of photodiodes array operating at 200 K HS MCT MBE were used with special composition distribution of composition throughout the thickness.

Mercury cadmium telluride surface passivation by the thin alumina film atomic-layer deposition

We analyzed the C-V curves of CdхHg1-хTe-based (x ∼ 0.22) MIS structures with Al2O3 as an insulator. Alumina films were deposited on p and n type CdхHg1-хTe by atomic layer deposition. C-V curve specific features at high and low frequencies were found to be a result of the semiconductor-dielectric interface surface state influence. The surface state density was derived from the fitting experimental C-V curves at high and low frequencies with the theoretical model. The calculated curves were obtained by solving Poisson and continuity equations within the drift-diffusion model. The charge exchange between the surface states and permitted bands was supposed to be conducted using the Shockley-Read-Hall mechanism.

The electrical properties of HgCdTe layers grown by MBE on Si and P + / n junction formed on its basis

We studied the electrical properties of undoped and indium-doped and arsenic-doped CdXHg1-XTe layers with x ≈ 0.3 - 0.4 grown by molecular beam epitaxy on Si (310) substrates. After the growth HgCdTe layers were annealed at mercury atmosphere. The lifetime at room temperature in the As-doped layers, do not depend on its carrier concentration. The lifetime in indium-doped layers increased after annealing at saturated mercury vapor pressure. It is explained by suppression of recombination centers density. Temperature dependence of the reverse currents of p+-n junctions fabricated in Cd0.3Hg0.7Te heterostuctures grown by MBE on Si substrates has been studied.

The 4×288 linear FPA on the heteroepitaxial Hg 1-x Cd x Te base

x4×288 heteroepitaxial mercury-cadmium telluride (MCT) linear arrays for long wavelength infrared (LWIR) applications with 28×25 micron diodes and charge coupled devices (CCD) silicon readouts were designed, manufactured and tested. MCT heteroepitaxial layers were grown by MBE technology on (013) GaAs substrates with CdZnTe buffer layers and have cutoff wavelength λco ≈ 11.8 μm at T = 78 K. To decrease the surface influence of the carriers recombination processes the layers with composition changes and its increase both toward the surface and HgCdTe/CdZnTe boundary were grown. Silicon read-outs with CCD multiplexers with input direct injection circuits were designed, manufactured and tested. The testing procedure to qualify read-out integrated circuits (ROICs) on wafer level at T = 300 K was worked out. The silicon read-outs for 4×288 arrays, with skimming and partitioning functions included were manufactured by n-channel MOS technology with buried or surface channel CCD register. Designed CCD readouts are driven with four- or two-phase clock pulses. The HgCdTe arrays and Si CCD readouts were hybridized by cold welding indium bumps technology. With skimming mode used for 4×288 MCT n-p-junctions, the detectivity was about (formula available in paper) for background temperature Tb = 295 K.

IR photodetector arrays based on HgCdTe films and GaAs/AlGaAs multiquantum wells

A technology was designed and the photodetector modules were manufactured for the 3-5 and 8-12 micrometers spectral range based on the Hg1-xCdxTe/GaAs heterostructures and GaAs/AlGaAs multiquantum well structures grown by the molecular beam epitaxy method. The photosensitive HgCdTe layers were grown on the GaAs substrates with the intermediate buffer layer of CdZnTe. To decrease the surface influence on the recombination processes graded gap HgCdTe layers with the increase to the surface composition were grown. A silicon multiplexer was designed and manufactured on the CMOS/CCD technology with frame rate 50 Hz. Hybrid assembly of the photodetectors array and the multiplexer was produced by the group cold welding on the indium bumps with control of the connection process. The manufactured 128 x 128 FPAs on the HgCdTe with the cut- off wavelength 6 micrometers and 8.7 micrometers had the NEDT value 0.02 K and 0.032 K, correspondingly, at operating temperature 78K and frame rate 50Hz. The photosensitive GaAs/AlGaAs multiquantum well structures were manufactured by the MBE method. It is shown that the designed technology allows to produce 129 x 128 photodetector arrays ((lambda) max=8 mum) with the NEDT value 0.021 K and 0.06 K at operating temperature of 54 K and 65 K, correspondingly.