MBE P-on-n Hg1−xCdxTe heterostructure detectors on silicon substrates

The capability of growing state-of-the-art middle wavelength infrared (MWIR)-HgCdTe layers by molecular beam epitaxy (MBE) on large area silicon substrates has been demonstrated. We have obtained excellent compositional uniformity with standard deviation of 0.001 with mean composition of 0.321 across 1.5″ radii. R₀A as high as 5 × 10⁷ ω-cm² with a mean value of 7 × 10⁶ Θ-cm² was measured for cut-off wavelength of 4.8 μm at 77K. Devices exhibit diffusion limited performance for temperatures above 95K. Quantum efficiencies up to 63% were observed (with no anti-reflection coating) for cut-off wavelength (4.8–5.4) μm @ 77K. Excellent performance of the fabricated photodiodes on MBE HgCdTe/CdTe/Si reflects on the overall quality of the grown material in the MWIR region.     

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.     

碲溶剂法生长高均匀性Hg1-xCdxTe体晶材料的工艺研究

通过改进碲溶剂长晶炉的径向炉温分布,改善了晶体生长的液-固界面,用碲溶剂长晶方法生长出了高均匀性碲镉汞体晶材料,用英国爱丁堡Mullard公司的碲镉汞晶片评价装置在光斑为1 mm2的测试条件下测出晶片材料组分均匀性(x为±0.003 mol.CdTe,达到了制作红外焦平面探测器列阵对材料的要求.     

Far infrared characterization of Hg1-xCdxTe and related electronic materials

Far infrared (10 to 250 cm⁻¹) reflection and transmission spectroscopy is used to characterize the free-carrier and alloy properties of the leading infrared detector material Hg_1-xCd_xTe and the substrate materials CdTe and CdZnTe. The data yield values for carrier concentration and mobility, the compositional parameter x and film thickness which generally agree with other determinations. The advantages of this contactless nondestructive technique are described. Applications to the newly proposed infrared detector material Hg_1-xMn_xTe are briefly reviewed.     

Growth by CVT and characterization of Hg1-xCdxTe epitaxial layers

Single crystal epitaxial layers of Hg_1-x Cd _x Te were grown on CdTe substrates employing the chemical vapor transport technique. Different growth temperatures, substrate orientations, and various pressures of Hgl₂ as a transport agent were used while the source materials had a fixed composition ofx = 0.2. The epilayers are of nearly uniform composition to a depth of about one-half of the layer thickness. Chemical etching of the as-grown epilayers revealed low etch pit densities in the range of 10³–10⁴ cm⁻². Rectangle-shaped etch pits are observed for the first time on the (100) oriented epilayers of this material. The growth temperature and Hgl₂ pressure used for the growth experiments have significant effects on the layer morphology and composition.     

非掺杂p型MBE—Hg1—xCdxTe材料的受主性质

对经２５０℃Ｐ型热处理获得的Ｈｇ１－ｘＣｄｘＴｅＭＢＥ材料进行变温霍耳测量和理论拟合计算，由此得到ＨｇＣｄＴｅ－ＭＢＥ材料的受主浓度为２－３×１０＾１６ｃｍ＾－３，残余施主浓度为５×１０＾１５ｃｍ＾－３左右，两才相比显示材料的补偿度较低，拟合得到的汞空位受主能级为１５－１８ｍｅＶdisplay structure     

Si基复合衬底碲镉汞液相外延技术的研究

文章报道了采用Si基复合衬底,利用液相外延方法成功进行中波碲镉汞薄膜生长的情况,并且采用X光双晶衍射、X光形貌、红外付立叶光谱仪等手段对碲镉汞薄膜进行了表征。Si基复合衬底碲镉汞外延膜晶体结构为单晶,并且它的双晶衍射半峰值接近国外同类产品的先进水平。     

Determination of cut-off wavelength and composition distribution in Hg1-xCdxTe

The determination of cut-off wavelength, λ _co, and composition distribution for Hg_1-xCd_xTe has been discussed in this paper. A shift of the cut-off wavelength was found from the photo-response calculation for the HgCdTe devices with the same energy gap E_g but different thickness d. An expression of λ _co(x,T,d) has been derived from the half-maximum photo-response curve calculation. The composition uniformity has been determined from the room-temperature transmission fitting procedure. The composition real space distribution is suggested to be determined by the combination of absorption edge phenomenon and thermal imaging technique.     

碲镉汞液相外延薄膜生长技术与性能

用液相外延的方法在ＣｄＺｎＴｅ衬底上生长Ｈｇ１－ｘＣｄｘＴｅ材料,获得了表面形貌好,位错密度低,组份均匀的碲匐汞外延材料,生长工艺对材料的参数控制有较好重复性,外延材料经热处理后,材料的Ｐ型和Ｎ型电学参数都达到较好的水平,并具有良好的可重复性。     

Process modeling of point defect effects in Hg1-xCdxTe

A model is presented which describes the motion of and interactions among some of the native point defects and foreign impurities in Hg_1-xCd_xTe. Semi-quantitative simulations of typical process problems are performed for cases where only Hg interstitials, Hg vacancies, and cation impurities are important. Results for the formation of n-on-p junctions by the Hg anneal of high vacancy concentration material, indicate that junction depths may be a significant function of the n-type dopant concentration. For the case where low vacancy, n-type material is annealed in a Hg-poor ambient, simulation results confirm the difficulty in forming a high quality, well-defined p-on-n junction. This difficulty arises because of the generation of Hg vacancy/interstitial pairs throughout the bulk during most of the process. It is demonstrated that impurity gettering can be described by our modeling approach. All simulation results attempted to date are consistent with the available experimental data.     

Process modeling and simulation for Hg1-xCdxTe. Part II: Self-diffusion,interdiffusion, and fundamental mechanisms of point-defect interactions in Hg1-xCdxTe

The Hg_0.8Cd_0.2Te type-conversion, Hg self-diffusion and interdiffusion processes are analyzed in the context of a first order reaction kinetics approach. Sets of nonlinear, stiffly coupled continuity equations are presented which describe the underlying physics, and their solutions model the observed macroscopic behavior. It is demonstrated that the Frenkel pair mechanism interactions dominated by the cation sublattice, in conjunction with basic diffusive and drift properties of the ionized point defects, comprise the basic processes which effect all macroscopic phenomena discussed. Existing experimental results are reviewed and apparent discrepancies discussed. Use is made of the Stanford University mercury cadmium telluride process simulator to provide quantitative and insightful examples of important results.     

空间用1.6μmHg1—xCdxTe室温光伏探测器

报道敢采用改进的区熔工艺生长的三元系金属化合物半导体ＨｇＣｄＴｅ材料研制的短波光伏探测器，其工作温度为室温，在响应波段１．５８－１．６４μｍ内探测率优于３．０×１０＾－１１ｃｍＨｚ＾１／２Ｗ＾－１，量子效率达７０％。暗电流主要受制于扩散电流与产生复合电流，器件经环境模拟试验，定标与联试，完全符合空间工程应用的要求。     

Current mechanisms in VLWIR Hg1−xCdxTe photodiodes

VLWIR (_c∼15 m to 17 m at 78 K) detectors have been characterized as a function of temperature to determine the dominant current mechanisms impacting detector performance. I_d−V_d curves indicate that VLWIR detectors are diffusion limited in reverse and near zero bias voltages down to temperatures in the 40 K range. At 30 K the detectors are limited by tunneling currents in reverse bias. Since the detectors are diffusion limited near zero bias down to 40 K, the R₀A_imp versus temperature data represents the diffusion current performance of the detector as a function of temperature. The detector spectral response measurement and active layer thickness are utilized to calculate the HgCdTe layer x value and the optical activation energy E_{a optical}. The activation energy, E_{a electrical}, obtained from the measured diffusion limited R₀A_imp versus temperature data is not equal to the activation energy, E_{a optical}, obtained from the spectral response measurement for all x values measured. E_{a electrical}=^*E_{a optical}, where ranges between 0.64 and 1.0 For cutoff wavelengths in the 9 m at 78 K, E_{a electrical}=E_{a optical}. E_{a electrical}=0.65^* E_{a optical} have been measured for_c=17 m at 78 K detectors. As the band gap energy decreases to values in the range of 70 meV and lower, it is reasonable to expect a more dominant role of band tailing effects on the transport properties of the material system. In such a picture, one would expect the optical band gap to be unmodified, whereas the intrinsic concentration could be enhanced from its value for the ideal semiconductor. Such a picture could explain the observed behavior. Further probing experiments and modeling efforts will help clarify the physics of this behavior.     

Independently accessed back-to-back HgCdTe photodiodes: A new dual-band infrared detector

We report the first data for a new two-color HgCdTe infrared detector for use in large dual-band infrared focal plane arrays (IRFPAs). Referred to as the independently accessed back-to-back photodiode structure, this novel dual-band HgCdTe detector provides independent electrical access to each of two spatially collocated back-to-back HgCdTe photodiodes so that true simultaneous and independent detection of medium wavelength (MW, 3–5 μm) and long wavelength (LW, 8–12 μm) infrared radiation can be accomplished. This new dual-band detector is directly compatible with standard backside-illuminated bump-interconnected hybrid HgCdTe IRFPA technology. It is capable of high fill factor, and allows high quantum efficiency and BLIP sensitivity to be realized in both the MW and LW photodiodes. We report data that demonstrate experimentally the key features of this new dual-band detector. These arrays have a unit cell size of 100 x 100 μm², and were fabricated from a four-layer p-n-N-P HgCdTe film grown in situ by metalorganic chemical vapor deposition on a CdZnTe substrate. At 80K, the MW detector cutoff wavelength is 4.5 μm and the LW detector cutoff wavelength is 8.0 μm. Spectral crosstalk is less than 3%. Data confirm that the MW and LW photodiodes are electrically and radiometrically independent.     

Hg1-xCdxTe光伏探测器的钝化研究

用倒易二维点阵对HgCdTe光伏探测器钝化及其热处理行为进行了研究,发现测射沉积的钝化膜会引起HgCdTe的晶面弯曲,严重的会出现晶面扭曲和mosaic结构,而钝化后的热处理能改善MCT晶体的完整性,在不同的钝化介质层钝化MCT的研究中发现,ZnS钝化层在高温下并不稳定,而CdTe钝化层却能保持较高的耐温性能。     

Molecular beam epitaxy HgCdTe growth-induced void defects and their effect on infrared photodiodes

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.     

Effect of dislocations on performance of LWIR HgCdTe photodiodes

The epitaxial growth of HgCdTe on alternative substrates has emerged as an enabling technology for the fabrication of large-area infrared (IR) focal plane arrays (FPAs). One key technical issue is high dislocation densities in HgCdTe epilayers grown on alternative substrates. This is particularly important with regards to the growth of HgCdTe on heteroepitaxial Si-based substrates, which have a higher dislocation density than the bulk CdZnTe substrates typically used for epitaxial HgCdTe material growth. In the paper a simple model of dislocations as cylindrical regions confined by surfaces with definite surface recombination is proposed. Both radius of dislocations and its surface recombination velocity are determined by comparison of theoretical predictions with carrier lifetime experimental data described by other authors. It is observed that the carrier lifetime depends strongly on recombination velocity; whereas the dependence of the carrier lifetime on dislocation core radius is weaker. The minority carrier lifetime is approximately inversely proportional to the dislocation density for densities higher than 10⁵ cm⁻². Below this value, the minority carrier lifetime does not change with dislocation density. The influence of dislocation density on the R₀A product of long wavelength infrared (LWIR) HgCdTe photodiodes is also discussed. It is also shown that parameters of dislocations have a strong effect on the R₀A product at temperature around 77 K in the range of dislocation density above 10⁶ cm⁻². The quantum efficiency is not a strong function of dislocation density.     

MBE HgCdTe heterostructure p-on-n planar infrared photodiodes

We recently succeeded in fabricating planar Hg_1−yCd_yTe/Hg_1−xCd_xTe (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/Hz^0.5 at 77K. Average R_oA 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 R_oA 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.     

Hg1-xCdxTe光伏探测器的表面漏电流机制及其钝化

表面漏电流能对Hg1-xCdxTe光伏探测器性能产生很大的影响,因此选择合适的钝化工艺尤其重要。本文主要论述了Hg1-xCdxTe光伏探测器表面漏电流机制及其钝化技术的发展状况。     

Growth and properties of Hg1-xCdxTe on GaAs,with x − 0.27

The organometallic vapor phase epitaxy of HgCdTe onto (100)2°-(110) GaAs substrates is described in this paper. A buffer layer of CdTe has been grown prior to the growth of HgCdTe, to take up the large lattice mismatch with the GaAs. Considerations for the thickness of this buffer layer are outlined, and it is shown by quantitative Secondary Ion Mass Spectroscopy that there is negligible diffusion of gallium from the GaAs substrate for the growth conditions described. Hall effect measurements give mobilities comparable to those reported for bulk grown crystals. An extrinsicn-type carrier concentration of 2 × 10¹⁶/cm³ is obtained, and is mainly due to residual impurities in the starting chemicals. The alloy composition has been determined at 298 K by Fourier transform infrared transmission (FTIR) spectrometry; this is found to be extremely uniform over a 15 × 7 mm area, as evidenced by an overlapping of FTIR plots taken over this area. HgCdTe layers have been grown on buffer layers varying in thickness from 0.1 to 1.9μm. It is found that a buffer thickness of about 1.9μm or larger is required to obtain high quality HgCdTe, both in terms of the electrical characteristics (mobility and carrier concentration) and the infrared transmission curves (peak transmission).