S. H. Shin

Characterization of Te precipitates in CdTe crystals

Te precipitates in CdTe have been characterized by Auger spectroscopy, x‐ray diffraction, and Raman spectroscopy. The x‐ray results show that the precipitated Te in Bridgman‐grown CeTe crystals has the same structural phase as observed in elemental Te under high pressure. Auger and Raman microprobe spectroscopy were carried out to confirm Te precipitates in CdTe and identify the symmetry of the Te precipitates.

Planar p‐on‐n HgCdTe heterostructure photovoltaic detectors

We report a process to fabricate planar Hg1−yCdyTe/Hg1−xCdxTe (x<y) heterostructure photodiodes with the p‐on‐n configuration. The material used for this demonstration was grown by molecular beam epitaxy. The p‐on‐n planar devices consist of an arsenic‐doped p‐type epilayer (y=0.28) on top of a long wavelength infrared n‐type epilayer (x=0.225, λ=10 μm). The planar junctions were formed by selective pocket diffusion of arsenic deposited by ion implantation. The detailed analysis of the current‐voltage characteristics of these diodes as a function of temperature show that they have high performance and that their dark currents are diffusion limited down to 52 K. The results also show that the R0A values for these devices are highly uniform at 77 K.

Long and middle wavelength infrared photodiodes fabricated with Hg1−x CdxTe grown by molecular‐beam epitaxy

Long and middle wavelength infrared (LWIR, MWIR) p+‐n photodiodes have been fabricated with Hg1−xCdxTe (0.20<x<0.30) grown by molecular‐beam epitaxy (MBE). The epilayers were grown on (211)B lattice‐matched ZnCdTe substrates. The surface morphology was smooth and free of in‐plane twins. The Cd concentration (x) was uniform across the wafer, with standard deviations (Δx) as low as 0.0017. Structural properties were measured by double‐crystal x‐ray rocking curve and dislocation etching; FWHM values as low as 34 arcsec and etch pit density values as low as 1×105 cm−2 were measured. p+ ‐n homojunctions were formed by arsenic diffusion; unpassivated mesa photodiodes were fabricated by standard photolithographic techniques. MWIR and LWIR photodiodes fabricated with MBE material exhibited good diode performance, comparable to that obtained on photodiodes fabricated with the more matured technique of liquid‐phase epitaxy. 77‐K R0A products of the diodes measured were 6.35×107, 22.3, and 1.76 Ω cm2 with cutoff wav...

HgCdTe double heterostructure injection laser grown by molecular beam epitaxy

While a variety of light‐detecting devices have been made with HgCdTe, little has been done to apply this technology to light‐emitting devices. We report here the successful fabrication and operation of the first HgCdTe injection laser. This stripe‐geometry double‐heterostructure laser was operated under pulsed current at temperatures between 40 and 90 K. At 77 K, the emission wavelength was 2.86 μm with a linewidth of 0.3 meV, and the pulsed threshold current density was 625 A/cm2. The double heterostructure, with a 1.4‐μm‐thick active layer, was grown and in situ doped by molecular beam epitaxy (MBE). The p+ and n+ confinement layers were doped with arsenic and indium, respectively.

Molecular‐beam epitaxy growth and in situ arsenic doping of p‐on‐n HgCdTe heterojunctions

In this paper we present, results on the growth of in situ doped p‐on‐n heterojunctions on HgCdTe epilayers grown on (211)B GaAs substrates by molecular‐beam epitaxy (MBE). Long wavelength infrared (LWIR) photodiodes made with these grown junctions are of high performance. The n‐type MBE HgCdTe/GaAs alloy epilayer in these structures was grown at Ts=185 °C and it was doped with indium (high 1014 cm−3 range) atoms. This epilayer was directly followed by the growth, at Ts=165 °C, of an arsenic‐doped (1017–1018 cm−3 ) HgTe/CdTe superlattice structure which was necessary to incorporate the arsenic atoms as acceptors. After the structure was grown, a Hg annealing step was needed to interdiffuse the superlattice and obtain the arsenic‐doped p‐type HgCdTe layer above the indium‐doped layer. LWIR mesa diodes made with this material have 77 K R0A values of 5×103, 81, 8.5, and 1.1 Ω cm2 for cutoff wavelengths of 8.0, 10.2, 10.8, and 13.5 μm, respectively; the 77 K quantum efficiency values for these diodes were gre...

Infrared diodes fabricated with HgCdTe grown by molecular beam epitaxy on GaAs substrates

Infrared photodiodes fabricated with HgCdTe epilayers grown on GaAs substrates by molecular beam epitaxy (MBE) are reported here for the first time. Growth was carried out on the (211)B orientation of GaAs, and the as‐grown epilayer (x=0.24) was p type. The n‐p junction was formed by Be ion implantation, the resistance‐area product (R0 A) at zero bias was 1.4×103 Ω cm2 , the wavelength cutoff was 8.0 μm, and the quantum efficiency was 22%; all were measured at 77 K. We show that in the diffusion regime diodes fabricated with MBE HgCdTe/GaAs have comparable R0 A product values to those made with HgCdTe grown by bulk techniques. This result discloses new possibilities for advanced monolithic HgCdTe devices based on GaAs integrated circuit technology.

Effect of the dislocation density on minority‐carrier lifetime in molecular beam epitaxial HgCdTe

The photoconductive minority‐carrier lifetime has been measured as a function of temperature and etch‐pit density in n‐type HgCdTe grown by molecular beam epitaxy with a composition range x=0.22–0.23 to determine the limiting recombination mechanisms, particularly those related to dislocation density. In the extrinsic region at temperatures T<77 K, the minority‐carrier lifetime is limited by Shockley–Read recombination. Strong correlation between minority‐carrier lifetime and dislocation density is observed.

Open‐tube isothermal vapor phase epitaxy of Hg1−xCdxTe on CdTe

Device‐quality Hg1−xCdxTe (0.2≤x≤0.35) epitaxial layers have been grown on CdTe substrates by open‐tube isothermal vapor phase epitaxy (ISOVPE). The surface morphology of the layers is mirrorlike, and the Hall data are comparable to those for HgCdTe grown by liquid phase epitaxy (LPE). Photovoltaic devices with a cutoff wavelength of 4.1 μm at 77 K were fabricated on an ISOVPE HgCdTe epilayer. Their performance is comparable with those that we have obtained for such devices fabricated on LPE HgCdTe epilayers.

HgCdTe/CdTe heterostructure diodes and mosaics

This paper discusses the results of a study of the properties of HgCdTe/CdTe heterostructure diodes and mosaics. In this study, p-type HgCdTe epi-layers on the order of 20 µm were grown on CdTe substrates by a liquid-phase epitaxial (LPE) technique. These layers normally had a carrier concentration of 5 × 1016/cm3and a mobility of 400 cm2/V . s at 77 K. The n+-p junction was formed by boron ion implantation, and standard photolithographic techniques were used for the device fabrication. The diodes with no antireflection coating had a typical quantum efficiency of 40 percent. The 1/fnoise knee was on the order of 10 Hz at zero bias. Surface leakage seemed to be the dominant component for diodes at temperatures less than 77 K. From mosaic studies, it was found that the spectral spread was less than ±0.3 µm for an area as large as 12 × 20 mm. The study indicates that LPE offers a viable technique for producing high-quality HgCdTe epi-layers on CdTe.

1.33‐μm HgCdTe/CdTe photodiodes

Hg1−xCdxTe epilayers with a wavelength of ∼1.33 μm have been successfully grown by liquid phase epitaxy. Photodiodes were fabricated and measured. Analysis of the heterojunctions indicates that at room temperature the junction current at forward bias is dominated by a generation‐recombination mechanism. The generation‐recombination effective lifetime was estimated to be 2×10−7 s. A leakage current density of 9×10−6 A/cm−2 was observed at a reverse bias of 30 V, and the diode breakdown voltage was 70 V.