Doping Of HgCdTe Research Articles

HgCdTe high operation temperature infrared detectors

Based on the current development direction of infrared detector technology. The advantages of HgCdTe high operation temperature (HOT) infrared detector were analyzed in terms of module weight, shape size, power consumption, environmental adaptability and reliability from the perspective of application requirements of HOT infrared detector. The technical route and research status of HgCdTe HOT infrared detector in Europe and America were summarized. From the perspective of device dark current and noise mechanism, the change of dark current and noise at different operating temperatures and their effects on device performance were analyzed. The basic principles of the process optimization HgCdTe devices based on Hg vacancy n-on-p structure, extrinsic doped HgCdTe HOT devices based on in-doped p-on-n structure and Au doped n-on-p structure, nBn based HOT devices based on barrier structure and non-equilibrium mode HgCdTe HOT devices based on thermally excited carrier auger suppression in absorption layer were summarized. The performance of HgCdTe HOT devices with different technology routes and the technical difficulties in the preparation of detectors were compared and analyzed. Based on the comprehensive analysis of the performance and technical difficulties of HOT devices with different technology routes, the future development direction of HgCdTe HOT device technology was prospected. It is considered that the fully depleted device based on low concentration doping absorption layer has better development potential.

Electrical and Optical Studies of Defect Structure of HgCdTe Films Grown by Molecular Beam Epitaxy

Electrical and optical studies of defect structure of HgCdTe films grown by molecular beam epitaxy (MBE) are performed. It is shown that the peculiarity of these films is the presence of neutral defects formed at the growth stage and inherent to the material grown by MBE. It is assumed that these neutral defects are the Te nanocomplexes. Under ion milling, they are activated by mercury interstitials and form the donor centers with the concentration of 1017 cm–3, which makes it possible to detect such defects by measurements of electrical parameters of the material. Under doping of HgCdTe with arsenic using high temperature cracking, the As2 dimers are present in the arsenic flow and block the neutral Te nanocomplexes to form donor As2Te3 complexes. The results of electrical studies are compared with the results of studies carried out by micro-Raman spectroscopy.

Incorporation and activation of arsenic in MBE-grown HgCdTe

Research into p-type doping of HgCdTe with arsenic has concentrated on the use of a conventional effusion cell and optimization of growth conditions to achieve an increase in incorporation efficiency. This study investigates the use of a cracker cell, which is now the preferred method of doping HgCdTe due to its higher arsenic incorporation efficiency under optimum growth conditions. A detailed investigation of a number of arsenic doped HgCdTe layers grown on CdZnTe substrates by molecular beam epitaxy using a cracker cell as a source of arsenic is presented. Growth parameters influencing the amount of arsenic incorporated, such as the cracker-cell bulk temperature and substrate temperature, were investigated. Arsenic depth profiles were obtained via detailed secondary ion mass spectrometry where all major constituents in the epilayers were analysed. Magneto-transport Hall measurements were performed on as-grown material and those that underwent high-temperature anneals typical for arsenic activation. Using the quantitative mobility spectrum analysis technique, contributions to total conductivity arising from various carriers present in the samples have been separated. As-grown samples were found to exhibit n-type behaviour consistent with arsenic incorporating on cation sublattice, while samples that underwent high-temperature annealing show partial activation of arsenic with electron compensation.

Precise arsenic doping of HgCdTe by MBE and effects on compositional interdiffusion

Characterization data are presented for arsenic-doped Hg1−xCdxTe epilayers, grown on CdZnTe substrates by molecular beam epitaxy. Arsenic incorporation is influenced both by the cracker-cell bulk temperature (As flux) and by the substrate surface temperature. An Arrhenius-type equation can be used to fit the As incorporation data, yielding characteristic energies of 1.54 and 6.61 eV for the As cell and HgCdTe surface temperatures, respectively, independent of alloy fraction. This relation allows significantly improved predictability and control in the As doping concentration. The effect of growth temperature on As incorporation is demonstrated using a multilayer test structure with composition stepped in a sequence, with x=0.6, 0.45, 0.3, 0.2, of n-type material, followed by the reverse sequence of As-doped material, with the As cell temperature held constant. Secondary ion mass spectroscopy profiles of this layer again indicate the strong As incorporation dependence on growth temperature. Composition profiles for as-grown and annealed pieces of the multilayer sample show greater interdiffusion for the As-doped region as compared to the undoped region, which is attributed to the Fermi-level enhancement effect.

Model for minority carrier lifetimes in doped HgCdTe

We calculate the radiative, Auger, and the Shockley-Read-Hall recombination rates with Fermi-Dirac statistics and accurate band structures to explain the measured temperature dependence and doping dependence of minority carrier lifetimes in three n- and one p-type sample. We show that a trap state tracking the conduction band edge with very small activation energy can explain the lifetimes in the n-doped samples considered here. Similarly, for moderately p-doped HgCdTe alloy, a trap level at 75 meV is needed to explain the observed lifetimes. In either case, movement of Fermi level with respect to the trap level explains the temperature dependence of the lifetimes.

A discussion on the utilization of elemental transmutation for efficient p-type doping in HgCdTe and HgCdTeSe: Approach and methodology

For p-type doping of HgCdTe, As is preferred because of its relatively low diffusion coefficient, but it suffers from being amphoteric. In this paper, two possible techniques for incorporating As into HgCdTe that should ensure its presence only on nonmetal sites are presented and discussed. These methods are primarily based on the fact that Se can be readily incorporated into group VI sites and that 75Se naturally decays into 75As. Because the nuclear recoils associated with this decay are too small to displace arsenic atoms, substitutional p-doping should be ensured. In addition, a methodology for accurately determining the efficiency of these doping techniques and their influence on the electrical and optical properties of the material is presented.

Comment on ‘‘Temperature limits on infrared detectivities of InAs/InxGa1−xSb superlattices and bulk Hg1−xCdxTe’’ [J. Appl. Phys. 74, 4774 (1993)

Three papers published recently [P. M. Young, C. H. Grein, H. Ehrenreich, and R. H. Miles, J. Appl. Phys. 74, 4774 (1993); G. M. Williams, J. Appl. Phys. 77, 4153 (1995); C. H. Grein, M. E. Flatte, H. Ehrenreich, and R. H. Miles, J. Appl. Phys. 77, 4156 (1995)] concerning the comparison of theoretically predicted performance of HgCdTe photodiodes with InAs/InGaSb superlattice photovoltaic detectors are obscure with respect to optimal selection of HgCdTe photodiode structures. Both Comments [G. M. Williams, J. Appl. Phys. 77, 4153 (1995); C. H. Grein, M. E. Flatte, H. Ehrenreich, and R. H. Miles, J. Appl. Phys. 77, 4156 (1995)] have not noticed the important results of papers published by Humpreys [Infrared Phys. 23, 171 (1983); Infrared Phys. 26, 337 (1986)], who critically reexamined the role of a radiative mechanism in the detection of infrared radiation. To explain our point of view on competition between InAs/InGaSb SLs and ‘‘bulk’’ HgCdTe detectors, we present a generalized model of an infrared photodetector and derive the figure merit of any material for infrared photodetector as the ratio of absorption coefficient to the thermal generation rate. This determines the detectivity of infrared photodetectors. Using that model for the most common n+-p and p+-n long wavelength HgCdTe photodiodes, it is shown that the highest performance can be obtained with a low doping of the base photodiode regions. This means that the previously assumed (Young et al.) highly doped HgCdTe photodiode structure with a thick base region is far from optimal. Our calculations carried out for optimal device structures indicate that the ultimate detectivities of long wavelength HgCdTe photodiodes operating at 77 K are higher than those for InAs/InGaSb SLs.

P-type doping of double layer mercury cadmium telluride for junction formation

Extrinsic p-type doping of long wavelength infrared-HgCdTe double layer heterostructure for p-on-n device application requires good control of the p-type dopant, regardless of the doping technique. The approach is to place the electrical junction ahead of the compositional interface, thus avoiding quantum efficiency reduction. This research addresses the As and P doping of HgCdTe by an implant/diffusion process. The data demonstrates an enhanced atomic diffusion process for As and P from an ion implanted source, within the single phase domain, with a diffusion rate orders of magnitude higher than the rate under Hg-saturated conditions at the same temperature. This work also reveals a new phenomenon, namely, a transition in the enhanced diffusion of both As and P from an exponential to a Gaussian redistribution. This transition is controlled by temperature at a given PHg. Gaussian diffusion dominates at high temperatures, T >400°C. The diffusion coefficient of the Gaussian mechanism decreases as the PHg increases, from Dp ~2 x 10-11 cm2/s at PHg ~0.02 atm to Dp ~3 x 10-14 cm2/ s under Hg-saturated conditions (quartz ampoule) at 440°C. The difference in the diffusion coefficients between open tube and closed tube (quartz ampoule), under nominally Hg-saturated conditions, indicates that PHg is undersaturated regardless of the Hg-source proximity. The deviation of PHg from saturation is estimated from the annealing furnace temperature profile up to a maximum of 50%. Variation of the diffusion coefficient close to Hg saturation appears to be sharply dependent on the actual PHg value (example: Dp ~1 x 10-12 cm2/s in open-tube anneal vs Dp ~3 x 10-14 cm2/s in closed tube at nominally the same temperature, T = 440°C). Comparative anneals of As and P showed faster diffusion rates for P than for As in both mechanisms.

Growth and properties of In- and As-doped HgCdTe by MBE

Electrical doping of II–VI compound semiconductors is a major issue in MBE growth, especially the p-type doping. In this paper, we will report on the molecular beam epitaxial growth and properties of In- (n-type) and As- (p-type) doped HgCdTe alloys. Unlike the CdTe/HgTe modulation doped approach, we have successfully developed a technique to dope HgCdTe with cadmium arsenide compound directly during the alloy growth. Electrical, optical, structural and chemical properties of these doped HgCdTe layers have been determined by a variety of techniques. The results indicate that these properties vary strongly with crystal orientations. The (211)B phase is a preferred orientation for the MBE growth. The success to control both n- and p-type doping using In and As, respectively, has led to the growth of double layer heterojunction structures for local plane array applications.

Diffusion of As and Sb in HgCdTe

This paper reports the diffusion mechanisms of ion-implanted As and Sb in HgCdTe, grown by metalorgic chemical vapor deposition (MOCVD), and on the application of the resultant findings to the As diffusion from a grown source. A diffusion model was developed from a chemical analysis using secondary ion mass spectroscopy (SIMS) and a Gaussian theoretical model. The nature of the As and Sb diffusion mechanism and the various components of the diffusion profile were investigated. The most controllable mechanism is found to be the atomic vacancy-based component in which As and Sb start on the Te sublattice. The associated diffusion coefficients of D 400° C =3 x10 -14 cm 2/s and D 450° C =2 x10 -13 cm 2/s for As and D 350° C = 0.9 x10 -14 cm 2/s, and D 400° C =4 x10 -13 cm 2/s for Sb were calculated from the experimental data. The dislocation density and its distribution were the main cause for the enhancement of As diffusion in the tailing components. The proper choice of ion implantation and anneal conditions reduced the tailing components of the diffusion profile for a given dislocation density. High performance p-on-n photodiodes at 77 K were demonstrated, using As diffusion, from implanted and grown source, into n-type In doped HgCdTe grown on GaAs/Si substrates.

HgCdTe 128×128 infrared focal plane arrays on alternative substrates of CdZnTe/GaAs/Si

High quality p-on-n heterojunction infrared detectors have been fabricated using controllably doped HgCdTe grown by liquid phase epitaxy on CdZnTe/GaAs/Si alternative substrates grown by metalorganic chemical vapor deposition and used to demonstrate the first 128×128 focal plane array fabricated on these materials. Detectors with a cutoff wavelength of 6.0 μm and a resistance-area product R0 Aj average of 6.0×104 Ω cm2 at 80 K for 16 189 detectors in the array were achieved, and for operating temperatures above approximately 120 K were comparable in performance to detectors co-fabricated on standard lattice-matched bulk CdZnTe substrates. Below 120 K, detector performance was limited by excess generation-recombination current, probably caused by a higher threading dislocation density compared with that for the bulk substrates.

Annealing and electrical properties of organometallic vapor phase epitaxy–interdiffused multilayer process grown HgCdTe

The electrical properties of both undoped and doped HgCdTe epitaxial layers grown by organometallic vapor phase epitaxy (OMVPE) using the interdiffused multilayer process have been studied. Undoped, as‐grown layers exhibited anomalous Hall‐effect behavior. However, after annealing in mercury vapor, classical single‐carrier n‐type characteristics were obtained with residual electron concentrations as low as 4×1014 cm−3. Extrinsic doping of OMVPE layers has been demonstrated using alkyl dopant precursors for both n‐type doping with indium and for p‐type doping with either antimony or arsenic. The electrical properties of these doped films were relatively unchanged by further mercury vapor annealing.