Electroluminescence properties of PbTe pn junctions fabricated under controlled Te vapor pressures

Electroluminescence properties of PbTe pn junctions grown under various tellurium vapor pressures are investigated. For unintentionally doped pn junctions, the luminescence bands corresponding to D-A pair and band to band transition are observed. The luminescence intensity of the band to band transition has depended on tellurium vapor pressure, which suggests nonradiative transitions through nonstoichiometric defects forming deep levels. For pn junctions with Bi-doped epitaxial layers, only one peak appears at 20∼25 meV below band to band-transition energy, which, probably, shows recombination through impurity levels or impurity band originating from Bi-doping.     

Electroluminescence and lasing properties of highly Bi-doped PbTe epitaxial layers grown by temperature difference method under controlled vapor pressure

Electroluminescence (EL) from PbTe pn homojunctions with a highly Bi-doped n-type emission layer with a concentration of N_Bi > 10¹⁹ cm⁻³, grown by the temperature difference method (TDM) under controlled-Te vapor pressure has shown a positive shift of the peak-photon energy, which coincides with the model that Bi atoms act as both donors and acceptors, and they make the nearest lattice-site or very close donor-acceptor (DA) pairs. Broad-contact pn junctions with highly Bi-doped layers easily cause laser emission compared to the difficulty in the lasing operation of undoped pn junctions, which suggests that the nearest lattice-site Bi-Bi DA pairs act as strong radiative centers in PbTe.     

Properties of Bi-doped PbTe epitaxial layers and pn junction diodes grown by TDM-CVP

Effects of Bi-doping in PbTe liquid-phase epitaxial layers grown by the TDM-CVP have been investigated. For Bi concentration in the solution, x_Bi, lower than 0.2 at.%, Hall mobility is low. In contrast, for x_Bi>0.2 at.%, Hall mobility is high, while carrier concentration is in the range 10¹⁷ cm⁻³. However, ICP emission analysis shows that, for x_Bi=1.0 at.%, Bi concentration in epitaxial layer is N_Bi=2.3–2.7×10¹⁹ cm⁻³.These results indicate that Bi behaves not only as a donor but also as an acceptor; the nearest neighbor or very near DA pairs are formed. Carrier concentration for Bi-doped layers takes a minimum value at a Te vapor pressure of 2.2×10⁻⁵ Torr for growth temperature 470°C, which is coincident with that of the undoped PbTe. And broad contact pn junctions with highly Bi-doped layers easily cause laser emission compared to undoped junctions. The result suggests that the nearest lattice site Bi–Bi DA pairs behave as strong radiative centers in PbTe.     

Electrical properties of indium-doped LPE layers of Pb1−xSnx Te

Liquid-phase epitaxial (LPE) layers of Pb_1−xSn_xTe with an alloy composition 0≤×≤0.25 were doped n-type by adding from 0.002 to 10 at.% indium to the growth solution. Doping characteristics of indium and electrical properties of the epilayers at 77 and 4.2K were studied by Hall and resistivity measurements made directly on the grown layers. Electron concentration and mobility at 77 and 4.2K are presented as a function of indium doping for various x values. Doping coefficients of ~0.05 and ~0.03 are found for PbTe and Pb_0.8Sn_0.2Te, respectively, grown at ~450°C. For medium to high indium doping, the electron concentration saturates to a constant value independent of doping and LPE growth temperature. The saturation values decrease substantially with increasing x and increase with a decrease in sample temperature. Bulklike mobilities practically independent of doping are recorded up to an indium concentration N_ln~0.3 at.%, above which the mobility decreases with increasing indium concentration. The data shows that indium is a suitable donor in liquid-phase epitaxial layers of Pb_l-XSn_xTe.     

Properties of Bi-doped PbTe layers grown by liquid phase epitaxy under controlled Te vapor pressure

Effects of Bi doping in PbTe liquid-phase epitaxial layers grown by the temperature difference method under controlled vapor pressure (TDM-CVP) are investigated. For Bi concentrations in the solution, x_Bi, lower than 0.2 at.%, an excess deep-donor level (activation energy E_d≈0.03–0.04 eV) appears, and Hall mobility is low. In contrast, for x_Bi>0.2 at.%, Hall mobility becomes very high, while carrier concentration is in the range of 10¹⁷ cm⁻³. Inductive coupled plasma (ICP) emission analysis shows that, for x_Bi=1 at.%, Bi concentration in the epitaxial layer is as high as N_Bi=2.3–2.7 × 10¹⁹ cm⁻³. These results indicate that Bi behaves not only as a donor but also as an acceptor, and the nearest neighbor or very near donor-acceptor (D-A) pairs are formed, so that strong self-compensation of Bi takes place. Carrier concentration for highly Bi-doped layers shows a minimum at a Te vapor pressure of 2.2 × 10⁻⁵ torr for growth temperature 470°C, which is coincident with that of the undoped PbTe.     

Life time measurements in PbTe and PbSnTe

Experimental life time data of n-type PbTe and Pb_0.8Sn_0.2Te epitaxial layers are reported. Experiments were carried out with photoionized and impact ionized excess carriers between 6 and 300 K. Both materials show a strongly increasing life time with decreasing temperature. With PbTe an extremely non-exponential excess carrier decay was observed. Measurements of carrier sweep out and time resolved photo Hall effect have shown that in PbTe a strong minority carrier trapping occurs, whereas in PbSnTe, both electrons and holes, have nearly equal decay times. Comparing the experimental data with theory it can be concluded that in PbTe a Shockley-Read mechanism dominates the recombination at low temperatures. Auger recombination might become efficient only at temperatures above 200 K. The recombination behaviour in PbSnTe cannot be explained by one of the well-known models. An Auger recombination theory taking into account degeneracy might describe the observed data.     

Experimental determination of the mercury-rich corner of the Hg-Cd-Te phase diagram

Liquid-phase epitaxial (LPE) growth of Hg_1−xCd_xTe alloys from Hg-rich solutions has not been studied extensively owing to the relatively low solubilities of Cd and Te in this solvent system and the high vapor pressure of Hg. A vertical “infinite-melt” reflux LPE system is described which assures equilibrium between the liquid and vapor phases of Hg and is operable to 10 atm pressure, Using this system, the liquidus surface of the Hg-CdTe-HgTe phase field has been determined by solubility measurements of Te and CdTe in Hg for the 340°C to 520°C temperature range. Solidus isoconcentration lines in the range of 0.2 < × < 0.6 have been obtained by measurements of X as a function of depth for layers grown on single-crystal 〈111〉 oriented CdTe substrates. The experimental data thus obtained are in good agreement with theory. The general characteristics of LPE growth from Hg-rich solutions are discussed.     

Lasing properties of PbSnTe/PbTe double hetero mid-infrared laser diodes grown by temperature difference method under controlled vapor pressure liquid-phase epitaxy

PbSnTe/PbTe double hetero-diode structures were grown by temperature difference method under controlled vapor pressure (TDM–CVP) liquid-phase epitaxy (LPE). These laser diode (LD) structures were of the PbTe (Bi)/Pb_1−xSn_xTe/PbTe (undoped substrate) double hetero (DH) type. The peak shift of the wavelength emitted by the fabricated diodes was recorded and it was found that they successfully lased from 15 K to over 77 K (liquid nitrogen temperature) at a slightly lower threshold current density than standard LPEs fabricated via the slow-cooling method. In addition, the lasing peak wavelength was longer than spontaneous emissions. The laser spectra of diodes with varying Sn concentrations (x) in the active layer were observed, and their intensities were recorded as a function of the wavelength. Very sharp lasing spectra were obtained between 6.5 μm and 9.4 μm (x=0–0.11), clarifying that the stoichiometry control possible with TDM–CVP is suitable for fabricating optical devices. In addition, it was demonstrated that TDM–CVP is appropriate for fabricating infrared optical devices constructed from Pb_xSn_1−xTe systems.     

Slider LPE of Hg1-xCdxTe using mercury pressure controlled growth solutions

Homogeneous, nearly perfect single crystals of Hg_1-xCd_xTe are extremely difficult to prepare due primarily to the high vapor pressure of mercury. However, epitaxially grown Hg_1-xCd_xTe layers have a high potential for yielding material of a substantially higher quality. Using a new, open-tube, horizontal slider-type liquid phase epitaxial (LPE) growth technique, in which mercury pressure controlled growth solutions are used, a high degree of growth solution compositional control has been demonstrated. LPE layers of Hg_1-xCd_xTe have been grown on CdTe substrates and their high quality has been confirmed by optical, transport and electron microprobe measurements. Layer thicknesses are uniform and have been varied from 5 to 40 μ by changing the degree of supercooling or the growth time. An electron carrier concentration as low as 8.6 × 10¹⁵/cm³ and electron Hall mobilities up to 2.8 × 105 cm²/V-sec at 77K have been measured on in situ annealed samples. This work was sponsored by the Department of the Air Force and the U.S. Army Research Office.     

Liquid phase epitaxial growth and assessment of Pb1−xSn x Te alloys

The liquid-phase epitaxial growth of Pb_1−xSn_x Te on PbTe (100) substrates has been investigated over a range of growth temperatures from 600-400°C, and has been found to produce material with good uniformity and reproducibility of carrier concen-tration and alloy composition. The assessment of the epitaxial layers by such techniques as x-ray diffraction, dislocation etching and thermo-electric power measurements is described. Various features of the epitaxial layers such as interface irregularity, dislocation and diffusion effects are discussed, and likely mechanisms for their existence are proposed. The hole concentrations of the epitaxial layers, obtained by thermoelectric power measurements, are shown to have a similar dependence on preparation temperature as for bulk annealed material, suggesting that native defects are the dominant source of carriers above~ 2×10* cm^-3.     

Errata

The liquid-phase epitaxial growth of Pb_1−xSn_x Te on PbTe (100) substrates has been investigated over a range of growth temperatures from 600-400°C, and has been found to produce material with good uniformity and reproducibility of carrier concen-tration and alloy composition. The assessment of the epitaxial layers by such techniques as x-ray diffraction, dislocation etching and thermo-electric power measurements is described. Various features of the epitaxial layers such as interface irregularity, dislocation and diffusion effects are discussed, and likely mechanisms for their existence are proposed. The hole concentrations of the epitaxial layers, obtained by thermoelectric power measurements, are shown to have a similar dependence on preparation temperature as for bulk annealed material, suggesting that native defects are the dominant source of carriers above~ 2×10* cm^-3. The online version of the original article can be found at     

Au掺杂碲镉汞气相外延生长及电学性能

采用气相外延技术生长Au掺杂的Hg_(1-x)Cd_xTe薄膜材料,利用范德堡法对薄膜材料进行电学性能表征.通过变温霍尔测量,分析了常规Au掺杂p型薄膜的霍尔系数和霍尔迁移率随温度的变化,利用二次离子质谱(SIMS)分析薄膜中Au的纵向分布趋势.讨论了三种反常p型薄膜的霍尔系数和霍尔迁移率随温度的变化.通过变磁场霍尔测量,分析了具有反型层Hg_(1-x)Cd_xTe薄膜的迁移率谱,证实了由于表面电子、体电子以及体空穴混合导电造成的反常霍尔性能.     

Pb1-xSnxTe epitaxial layers prepared by the hot-wall technique

Epitaxial layers of Pb_1-xSn_xTe were grown on polished-etched KCl substrates using the modified hot-wall technique. Four layers, each 5-30 μm thick, of area 5.5 × 5.5 mm² were simultaneously grown at growth rates of 0.3–4.8 μm/hr. A typical substrate temperature of 325°C , and baffle and source temperatures of 450-560°C were used. P-and n-type layers were obtained from stoichio-metric and metal-rich sources of (Pb_1-xSn_x)_1+δ Te_1-δ, 0.01≤δ ≤0.02, respectively. From metal-rich sources with 0<δ<0.01, the layers obtained were n-type at 300K but p-type at 77K. The layers became intrinsic between approximately 250K and 295K. Carrier concentrations of as-grown layers with 0≤x ≤0.26 were in the range of 10¹⁶-10¹⁷ /cm³ and mobilities were of the order of 10⁴ cm² /V-sec at 77K. Both n-and p-type layers were also obtained from metal-rich sources of δ = 0.01 by controlling the Te vapor pressure from a separate reservoir. With Te temperatures higher than the n-p turnover point of 240°C , p-type characteristics were obtained. Layers that were p-type at 77K grown with the Te temperatures near the n-p turnover point had the best mirror-like surfaces.     

Metalorganic vapor phase epitaxy of (100) CdZnTe layers using diisopropylzinc source

Growth characteristics of (100) Cd_1−xZn_xTe (CZT) have been studied using metalorganic vapor phase epitaxy. CZT layers were grown on (100) GaAs substrates using diisopropylzinc (DiPZn), dimethylcadmiun (DMCd), and diethyltelluride (DETe) as precursors. Growths were carried out in the temperature range from 375 to 450°C. Since DiPZn has lower vapor pressure than DMCd, CZT layers with Zn composition below 0.06 were grown with good compositional control. Layers with uniform Zn composition and thickness over an area of 10 × 15 mm² were grown. Enhancement of CZT growth rate was observed when a small amount of DiPZn is introduced under fixed flows of DMCd and DETe. Zn composition increases abruptly for further increase of DiPZn flow rate, where growth rate decreases. Growth mechanisms for the above growth conditions were also discussed.     

Transient behavior of Hg1−xCdxTe film growth on (111)B CdTe substrates by chemical vapor transport

As part of a systematic investigation of the effects of substrate surfaces on epitaxial growth, the transient behavior of Hg_1−xCd_xTe film growth on (111)B CdTe by chemical vapor transport (CVT) has been studied as a function of growth time under vertical stabilizing (hot end on top) and vertical destabilizing (hot end at bottom) ampoule orientations. The experim ental results show the morphological transition of the Hg_1−xCd_xTe deposition on (111)B CdTe at 545°C from three-dimensional islands to layers within about 0.5 and 0.75 h for the growth under vertical stabilizing and destabilizing conditions, respectively. The combined effects of small convective flow disturbances on the growth morphology and defect formation are measurable. The overall trends of the time dependent growth rates and compositions of the Hg_1−xCd_xTe epitaxial layers under stabilizing and destabilizing conditions are similar. The system atically higher growth rates of the Hg_1−xCd_xTe films by about 10% under vertical destabilizing conditions could be influenced by a small convective contribution to the mass transport. The combined results show that improved Hg_1−xCd_xTe epitaxial layers of low twin density on (111)B CdTe substrates can be obtained by CVT under vertical stabilizing conditions.     

Effects of growth conditions on the composition of CVT and PVT grown Hg1-x Cd x Te epitaxial layers

Single crystal epitaxial layers of Hg_1-x Cd _x Te were grown on CdTe substrates employing the chemical and physical vapor transport techniques. Different growth temperatures and various pressures of HgI₂ as a transport agent were used while the source materials had compositions of eitherx = 0.4 orx = 0.6. The epilayers are of nearly uniform composition to a depth of about one-half of the layer thickness. The Hgl₂ pressure and the growth temperature used for the growth experiments have significant effects on the layer composition. The desired epilayer composition ofx = 0.2 can be achieved with either source compositions by properly adjusting the HgI₂ pressure and the growth temperature.     

Metalorganic vapor phase epitaxyin-situ growth of p-on-n and n-on-p Hg1-xCdxTe junction photodiodes using tertiarybutylarsine as the acceptor source

We report arsenic doping of Hg_1-xCd_xTe (0.2 < x < 0.3) grown using metalorganic vapor phase epitaxy (MOVPE) by the direct alloy growth (DAG) technique. Tertiarybutylarsine (TBAs) was used as a precursor for As doping. Several epilayers were grown at different Hg partial pressures and TBAs bubbler temperatures in order to study the doping characteristics. The amount of As incorporated in the layer as well as the acceptor concentration were found to be a strong function of the Hg pressure. Secondary ion mass spectrometric studies on heterostructures showed that the compositional interdiffusion is less than the diffusion of As during growth. P-N junctions were grown using TBAs for the first time and several of these layers were processed to fabricate photodiodes. A p-on-n grown junction photodiode with a cutoff wavelength of 8.2 μm had an R_oA value of 241 ohm-cm² at 80K and is the highest reported value for p-on-n DAG-MOVPE devices. Methods to improve the device R_oA of the grown junctions are also proposed.     

Investigations on low temperature mo-cvd growth of GaAs

The growth conditions for the deposition at low temperatures of epitaxial layers of GaAs on (100) GaAs crystals using TMG and arsine are studied in detail. The films are grown at atmospheric pressure in a vertical reactor in which the arsine is fed in through the rf heated susceptor for precracking. The growth temperature was varied between 680°C and 450°C. In the whole temperature range epitaxial growth was obtained. The growth rate at temperatures below 600°C depends on the AsH₃ flow, suggesting that the availibility of As vapor species, not AsH₃ limits epitaxial growth in this temperature range. For a constant AsH₃ /TMG ratio of 8 the growth rate decreases by exp (-E/kT) with an activation energy of E = 1.5 eV. Growth rates as low as 0.5 um/h have been achieved. Unintentionally doped layers show semi-insulating behaviour at growth temperatures below 500° C, similar to the behaviour seen from MBE layers. However, n-type layers with reasonable mobilities can be grown in the low temperature range (450 ° C) using H₂ Se as the doping gas.     

Growth and properties of Hg1-x Cdx Te epitaxial layers

The growth of epitaxial layers of mercury-cadmium-telluride (Hg_1-xCd_xTe) with relatively low x (0.2-0.3) from Te-rich solutions in an open tube sliding system is studied. The development of a semiclosed slider system with unique features permits the growth of low x material at atmospheric pressure. The quality of the films is improved by the use of Cd_1-yZ_yTe and Hg_1-xCd_xTe substrates instead of CdTe. The substrate effects and the growth procedure are discussed and a solidus line at a relatively low temperature is reported. The asgrown epitaxial layers are p-type with hole concentration of the order of 1·10¹⁷ cm⁻³, hole mobility of about 300 cm²·V⁻¹ sec⁻¹ and excess minority carrier life-time of 3 nsec, at 77 K.     

Open tube vapor transport growth of Pb1−xSnxTe epitaxial films for infrared detectors

Epitaxial films of Pb_1−xSn_xTe have been grown by open tube vapor transport on (100) Pb_1−xSn_xTe substrates. The as-grown films are suitable for detector array fabrication with respect to both surface smoothness and electrical properties. Charge compositions from 1% excess metal to 1% excess Te were used. Growth rates up to 3–4 ym per hour were achieved. The asgrown carrier concentrations varied from 3 × 10¹⁶cm⁻³ to 3 × 10¹⁷cm⁻³ depending on growth temperature and charge composition. Schottky barrier detectors with semi-transparent electrodes were fabricated on as-grown layers with no surface preparation. Good uniformity of detector parameters was obtained with arrays of 20 to 40 elements. The array size is not limited by either substrate size or epitaxial quality. Resistance-area products on the order of 1 ohm-cm were obtained at 77 K for detectors with a 12 ym long wavelength cutoff. Quantum efficiencies for 8–12 urn radiation were 40–50%. Peak response and 50% cutoff occurred at 11 and 12 ym, respectively. Uniformity of cutoff wavelength across the arrays of ± 0.1 ym was obtained.