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Publications (49)105.32 Total impact

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    ABSTRACT: Measurements of 77K RoA and 300K reverse bias dynamic impedance (RdA) products at one volt reverse bias has been carried out to assess the degree of correlation of this figure of merit. Planar P-on-n heterostructures were grown on near lattice-matched CdZnTe substrates with Hg1-xCdxTe (0.20< x <0.30) by molecular beam epitaxy. These devices were passivated with CdTe and doped with indium and arsenic as n- and p-type dopants, respectively. Current-voltage characteristic of these devices exhibit thermally generated dark currents at small and modest reverse bias. We have observed that RoA values of these long wavelength infrared P-on-n heterostructure photodiodes at 77K correlate with room temperature RdA values. Diode arrays with high room temperature RdA values at one volt reverse bias also have high RoA values at 77K. Similarly, low RdA values at room temperature indicate poor performance at 77K where deviation from diffusion current occurs at reverse bias of 0.2 to 1 volt at room temperature. The results presented here, for a small samples of devices, demonstrate that room temperature measurements of current-voltage characteristics to evaluate Hg1-xCdxTe (0.22< x <0.28) diode performance and array uniformity at lower temperatures can be used. This provides an acceptable criteria for further study at lower temperatures.
    Journal of Electronic Materials 04/1995; 24(5):681-684. · 1.64 Impact Factor
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    ABSTRACT: We have carried out a study and identified that MBE HgCdTe growth-induced void defects are detrimental to long wavelength infrared photodiode performance. These defects were induced during nucleation by having surface growth conditions deficient in Hg. Precise control and reproducibility of the CdZnTe surface temperature and beam fluxes are required to minimize such defects. Device quality material with void defect concentration values in the low 102 cm2 range were demonstrated.
    Journal of Electronic Materials 04/1995; 24(5):521-524. · 1.64 Impact Factor
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    ABSTRACT: 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.
    Journal of Electronic Materials 04/1995; 24(5):617-624. · 1.64 Impact Factor
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    ABSTRACT: Temperature and time dependent Hg-annealing studies for arsenic activation have been carried out on As-doped molecular beam epitaxy HgCdTe eitherin situ or by ion implantation to determine the extent of arsenic activation in the single layer. Enhanced As diffusion and activation in double layer heterostructures have also been investigated to further our understanding of the effects on zero bias resistance-area product (RoA) and quantum efficiency. The results show that the arsenic activation anneal is limited by Hg self-diffusion into the HgCdTe epilayer. Using this arsenic activation process for eitherin situ doped arsenic or implanted arsenic, high performance p-on-n double layer heterostructure photodiodes have been demonstrated on both mesa and planar device structures.
    Journal of Electronic Materials 01/1995; 24(5):609-615. · 1.64 Impact Factor
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    ABSTRACT: We recently succeeded in fabricating planar Hg1−yCdyTe/Hg1−xCdxTe (x<y) heterostructure photodiodes with the p-on-n configuration. Here we discuss early results in detail and present new results on an expanded range of infrared operation. The material used for this demonstration was grown by molecular beam epitaxy on lattice-matched CdZnTe substrates. The p-on-n planar devices consist of an arsenic-doped p-type epilayer (y∼0.28) atop a long wavelength infrared n-type epilayer (x=0.22–0.23). The planar junctions were formed by selective pocket diffusion of arsenic deposited on the surface by ion implantation. Detailed analysis of the current-voltage characteristics of these diodes as a function of temperature shows that they have high performance and that their dark currents are diffusion-limited down to 52K. Low frequency noise measurements at a reverse bias voltage of 50 mV resulted in noise current values (at 1 Hz) as low as 1×10−14 amps/Hz0.5 at 77K. Average RoA values greater than 106 Ω-cm2 at 40K were obtained for these devices with cut-off wavelength values in the 10.6 to 12 μm range. Seventy percent of these devices have RoA values greater than 105 Ω-cm2 at 40K; further studies are needed to improve device uniformity. These results represent the first demonstration that high performance long wavelength infrared devices operating at 40K can be made using HgCdTe material grown by a vapor phase epitaxy growth technique.
    Journal of Electronic Materials 07/1993; 22(8):1049-1053. · 1.64 Impact Factor
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    ABSTRACT: We report a process to fabricate planar Hg 1-y Cd y Te/Hg 1-x Cd x Te (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 R 0 A values for these devices are highly uniform at 77 K.
    Applied Physics Letters 04/1993; · 3.52 Impact Factor
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    ABSTRACT: We report the results of annealing effects on the As-doped alloy HgCdTe grown by molecular beam epitaxy (MBE), arsenic (As) diffusion in HgCdTe from Hg-rich solutions at low temperatures, and As ion implantation at room temperature. Hall-effect measurements, secondary ion mass spectrometry and p-on-n test photodiodes were used to characterize the As activation. High As-doping levels (1017−1019 cm−3) could be obtained using either MBE growth, As diffusion or As ion-implantation. Annealed below 400°C, As doping in HgCdTe shows n-type characteristics, but above 410°C demonstrates that all methods of As doping exhibit p-type characteristics independent of As incorporation techniques. For example, for samples annealed at 436°C (PHg≈2 atm), in addition to p-type activation, we observe a significant improvement of p/n junction characteristics independent of the As source; i.e. As doping either in situ, by diffusion, or ion implantation. A study of this As activation of As-doped MBE HgCdTe as a function of anneal temperature reveals a striking similarity to results observed for As diffusion into HgCdTe and implanted As activation as a function of temperature. The observed dependence of As activation on partial pressure of Hg at various temperatures in the range of 250 to 450°C suggests that As acts as an acceptor at high Hg pressure (>1 atm) and as a donor at low Hg pressure (<1 atm) even under Hg-rich conditions.
    Journal of Electronic Materials 01/1993; 22(8):1039-1047. · 1.64 Impact Factor
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    ABSTRACT: Transient minority carrier lifetime and steady state diffusion length measurements have been performed on n‐type HgTe/CdTe superlattices grown on CdZnTe(100) substrates. The n‐type (100) superlattice sample shows a lifetime of 90–100 ns at 77–160 K which then decreases with increasing temperature down to 50 ns near 300 K. p‐type HgTe/CdTe superlattices show normal behavior for temperature‐dependent lifetimes. The measured lifetime is approximately 20 ns at 77 K and increases continuously to 85 ns at 300 K. An independent measurement of minority carrier diffusion length in a p‐type HgTe/CdTe superlattice has led to an excellent agreement with a transient lifetime value of 66 ns at 200 K. The minority carrier diffusion length in a direction parallel to the interfaces indicates that the lateral transport properties are not much different from the transport properties of bulk HgCdTe.
    Applied Physics Letters 10/1992; · 3.52 Impact Factor
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    ABSTRACT: This study deals with the effects of perturbing the surfaces of unpassivated HgMnCdTe and HgCdTe short‐wavelength infrared photodiodes to further our understanding of these effects on dark currents. Perturbations include illuminating ultraviolet (UV) radiation in high vacuum and in various gaseous species. The change in dark current at 0.8 V reverse bias and its evolution with time was monitored in situ. By correlating the amount of excess dark current generated by UV radiation to the vacuum conditions, we conclude that it is a surface‐related problem. A drastic improvement in device performance was found by illuminating its surface with UV radiation in high vacuum. This simple treatment prevents the generation of excess and persistent dark current and stabilizes the leakage current at low reverse bias. This can be understood in terms of photodesorption of surface contaminants which induce deep level surface states, giving rise to the persistent dark current generation. By studying the effects of various gaseous species, we identified water molecules as the key surface contaminants. We also discovered an anomalous degradation in HgCdTe diodes when they were exposed to hydrogen and UV radiation simultaneously. This anomalous degradation can be interpreted as UV‐catalyzed chemical reduction of HgCdTe by hydrogen or the diffusion of hydrogen atoms into the bulk to change the junction characteristics.
    Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 08/1992; · 1.36 Impact Factor
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    ABSTRACT: Long‐wavelength infrared molecular‐beam epitaxial (MBE) HgCdTe films with dislocation densities as low as 2.3 × 10<sup>5</sup> cm<sup>-2</sup> on (211) GaAs and Si substrates have been obtained by postgrowth thermal annealing and thermal cycle annealing processes (300–490 °C). Experiments show that metalorganic chemical vapor deposition (MOCVD) HgCdTe epilayers require a higher thermal annealing temperature than MBE material and the difference in dislocation reduction between MBE and MOCVD HgCdTe materials is caused by dislocation movement under high‐temperature and thermal stress conditions. The CdTe buffer layer has been observed to play a significant role for the dislocation reduction in the HgCdTe epilayer grown on GaAs or Si alternative substrates. To study the role of dislocations on MBE HgCdTe/GaAs, systematic measurements of the minority carrier lifetime of MBE HgCdTe grown on both CdZnTe and GaAs substrates were carried out. A strong correlation between minority carrier lifetime and dislocation density is observed.
    Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 08/1992; · 1.36 Impact Factor
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    ABSTRACT: 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.
    Applied Physics Letters 12/1991; · 3.52 Impact Factor
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    ABSTRACT: 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/cm<sup>2</sup>. The double heterostructure, with a 1.4‐μm‐thick active layer, was grown and in situ doped by molecular beam epitaxy (MBE). The p<sup>+</sup> and n<sup>+</sup> confinement layers were doped with arsenic and indium, respectively.
    Applied Physics Letters 09/1991; · 3.52 Impact Factor
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    ABSTRACT: Post growth thermal annealing has been used to reduce the threading dislocation density of Hg 1-x Cd x Te (0.20≤x≤0.28) epilayers grown on (211)B GaAs substrates by molecular beam epitaxy. Etch pit density studies indicate an order of magnitude reduction on the surface threading dislocations after annealing at 490 °C for 30 min. The dislocation density at the HgCdTe surface on this highly mismatched system is only a factor of 2–6 times higher than the best values (1×10<sup>5</sup> cm<sup>-2</sup> ) we have obtained using CdZnTe bulk lattice‐matched substrates. The reduction of dislocations may be due to enhanced dislocation movement and their annihilation and coalescence at Hg vacancies point defect pinning centers introduced during the annealing process.
    Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 06/1991; · 1.36 Impact Factor
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    ABSTRACT: 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 T s =185 °C and it was doped with indium (high 10<sup>14</sup> cm<sup>-3</sup> range) atoms. This epilayer was directly followed by the growth, at T s =165 °C, of an arsenic‐doped (10<sup>17</sup>–10<sup>18</sup> cm<sup>-3</sup> ) 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 R 0 A values of 5×10<sup>3</sup>, 81, 8.5, and 1.1 Ω cm<sup>2</sup> 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 greater than 55%. These recent results represent a significant step toward the demonstration of MBE as a viable growth technique for the in situ fabrication of large area LWIR focal plane arrays.
    Journal of Applied Physics 03/1991; · 2.21 Impact Factor
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    ABSTRACT: In this paper we report on p‐type arsenic doping of CdTe and HgTe/CdTe superlattices by photoassisted and conventional molecular‐beam epitaxy (MBE). We also report on some of the problems involved in doping and growing the HgTe/CdTe superlattice system by theoretically examining two key aspects of its growth: (i) growth of CdTe at low temperatures under Cd‐stabilized conditions, and (ii) effect of laser excitation on the growing CdTe surface. p‐Type arsenic‐doped CdTe and HgTe/CdTe superlattice epilayers were grown on (100) CdTe and CdZnTe substrates at low temperatures under cation‐stabilized conditions obtained either with excess Cd, or excess Hg fluxes. As‐grown arsenic‐doped CdTe layers had room temperature carrier concentrations in the 10<sup>1</sup><sup>4</sup>–10<sup>1</sup><sup>6</sup> cm<sup>-</sup><sup>3</sup> range, and hole mobilities of about 35–65 cm<sup>2</sup>/V s. Low‐temperature photoluminescence spectra of arsenic‐doped CdTe epilayers grown by photoassisted MBE showed an emission peak at 1.51 eV, which is associated to the As Te acceptor (arsenic occupying a Te site) with a 92 meV ionization energy. CdTe epilayers grown at low temperatures with photoassisted MBE have superior structural, optical, and electrical properties than those grown by conventional MBE. Arsenic doping of the HgTe/CdTe superlattice structure has resulted in in situ growth of p‐type modulation‐doped superlattices with enhanced mobilities. Undoped superlattices grown under the same conditions are n‐type. These results represent a significant step towards the in situ fabrication of photodiodes and other advanced devices based on HgTe/CdTe doped superlattice structures.
    Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 04/1990; · 1.43 Impact Factor
  • J.M. Arias, S.H. Shin, E.R. Gertner
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    ABSTRACT: Reported here for the first time is the successful MBE growth of Hg1-xCdxTe (0.16 < x < 0.41) on the nonpolar (110) face of CdTe substrates. (110) HgCdTe epilayers always show p-type conductivity at 77 K with high hole concentration (1016-1019 cm-3) and good structural quality, as determined by double-crystal X-ray rocking curve (100–180 arc sec). We also report that during the MBE growth process, the rate of Hg vacancy formation on the (110) orientation is greater than on the more conventional (111)B and (100) orientations. The unique material properties of (110) HgCdTe may find application in the fabrication of photovoltaic detectors, light emitting diodes, and multiple quantum wells for nonlinear optics applications.
    Journal of Crystal Growth 01/1990; 86(s 1–4):362–366. · 1.55 Impact Factor
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    ABSTRACT: 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 (R 0 A) at zero bias was 1.4×10<sup>3</sup> Ω cm<sup>2</sup> , 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 R 0 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.
    Applied Physics Letters 04/1989; · 3.52 Impact Factor
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    ABSTRACT: Long and middle wavelength infrared (LWIR, MWIR) p<sup>+</sup>‐n photodiodes have been fabricated with Hg 1-x Cd x Te (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 1×10<sup>5</sup> cm<sup>-2</sup> were measured. p<sup>+</sup> ‐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 R 0 A products of the diodes measured were 6.35×10<sup>7</sup>, 22.3, and 1.76 Ω cm<sup>2</sup> with cutoff wavelengths of 4.66, 9.96, and 12.90 μm, respectively. The R 0 A product for a VLWIR photodiode was 1.36×10<sup>2</sup> Ω cm<sup>2</sup> with a cutoff wavelength of 16.23 μm at 35 K. LWIR diodes with no antireflection coating had a quantum efficiency of 48.6%. The present results represent a significant step toward the demonstration of MBE as a viable growth technique for the fabrication of large infrared focal plane arrays.
    Journal of Applied Physics 03/1989; · 2.21 Impact Factor
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    ABSTRACT: Device‐quality Hg 1-x Cd x Te (0.26≪x≪0.33) epilayers with thicknesses in the range 10–20 μm were grown on (111)B CdTe substrates by molecular beam epitaxy (MBE). The as‐grown layers were p type, and typically had carrier concentrations in the low 10<sup>1</sup><sup>6</sup> cm<sup>-</sup><sup>3</sup> range and hole mobilities greater than 220 cm<sup>2</sup>/V s at 77 K. The n<sup>+</sup>‐p junction was formed by Be ion implantation; unpassivated mesa photodiodes were fabricated by standard photolithographic techniques. Resistance‐area products (R 0 A) at zero bias were 5.2×10<sup>6</sup> and 1.4×10<sup>4</sup> Ω cm<sup>2</sup> at 77 K for Hg 1-x Cd x Te with cutoff wavelengths of 4.0 and 5.7 μm, respectively. These R 0 A values approach typical ones obtained by liquid phase epitaxy and represent a very promising initial effort for MBE‐grown Hg 1-x Cd x Te.
    Applied Physics Letters 02/1988; · 3.52 Impact Factor
  • J. M. Arias, S. H. Shin, E. R. Gertner
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    ABSTRACT: Reported here for the first time is the successful MBE growth of Hg(1-x)Cd(x)Te (x between 0.16 and 0.41) on the nonpolar (110) face of CdTe substrates. (110) HgCdTe epilayers always show p-type conductivity at 77 K with high hole concentration (10 to the 16th - 10 to the 19th/cu cm) and good structural quality, as determined by double-crystal X-ray rocking curve (100-180 arcsec). It is also reported that during the MBE growth process, the rate of Hg vacancy formation on the (110) orientation is greater than on the more conventional (111)B and (100) orientations. The unique material properties of (110) HgCdTe may find application in the fabrication of photovoltaic detectors, light emitting diodes, and multiple quantum wells for nonlinear optics applications.
    Journal of Crystal Growth 01/1988; 86:362-366. · 1.55 Impact Factor