R. G. Benz

Properties of undoped and Sb-doped CdTe surfaces prepared by conventional and photo-assisted molecular beam epitaxy

Abstract The effect of photo-illumination on the desorption activation energies for Cd, Te and Sb on (001)CdTe have been studied by reflection high energy electron diffraction. Within experimental error no effect was observed for Cd or Sb, but a large decrease was observed in the Te activation energy below 300°C. Thus laser-illumination enhances Te-desorption and produces more sites for Sb incorporation. Complementary Auger studies indicate a 20% increase in Sb adsorption due to Sb filing both photon desorbed Te-sites and some equilibrium Te-site vacancies.

Gas source iodine doping and characterization of molecular‐beam epitaxially grown CdTe

Investigations are reported on the gas source iodine doping of CdTe grown by molecular‐beam epitaxy, utilizing ethyliodide as the dopant precursor. Structural and electrical characterizations of these layers showed them to have favorable crystalline properties and indicated that the electrical activity of iodine in CdTe was between 50% and 100%. Electron concentrations between 6×1016 and 3×1018 cm−3 were obtained and showed the highest mobilities measured in epitaxial n‐type CdTe. These studies also showed that the incorporation of iodine was independent of the II/VI flux ratio and that its electrical activity was independent of both dopant concentration and II/VI flux ratio. The photoluminescence spectrum at 10 K was dominated by strong excitonic recombination bound to ionized and neutral iodine donors. These results demonstrate that iodine is a highly effective donor in CdTe.

Analysis of GaAs Substrate Removal Etching with Citric Acid : H 2 O 2 and NH 4 OH : H 2 O 2 for Application to Compliant Substrates

New properties associated with selective substrate removal have been observed in the application of this technique to GaAs thin film compliant substrates. Citric acid- and NH 4 OH-based etches are used to selectively etch the GaAs substrate and stop on an AlAs layer. The AlAs stop-etch layer is transformed into a layer that is almost twice as thick as the original layer, mismatched to the remaining GaAs epilayer, and has a refractive index around 2.0. Replacement of the single AlAs stop etch layer with multiple thin AlGaAs stop etch layers is proposed to alleviate this problem.

Ethyliodide n‐type doping of Hg1−xCdxTe (x=0.24) grown by metalorganic molecular beam epitaxy

Conductive n‐type Hg1−xCdxTe epitaxial layers with x=0.24 were grown by metalorganic molecular beam epitaxy using iodine doping. Ethyliodide was chosen as the dopant precursor based on previous results obtained for CdTe. The low‐temperature (20 K) electron concentration increased from an undoped level of ∼1015 cm−3 to 5×1018 cm−3 for ethyliodide flow rates from 10−4 to 10 sccm. High electron mobilities were measured and secondary ion mass spectrometry measurements indicated a high degree of electrical activity. These results demonstrate that iodine is a highly effective n‐type dopant for long‐wavelength HgCdTe alloys and device structures.

Chemical beam epitaxy of CdTe, HgTe, and HgCdTe

Abstract A chemical beam epitaxy (CBE) systems has been implemented for the growth of CdTe, HgTe, and their alloys. The system is briefly described. Results on the cracking of the organometallic source gases are presented. Epitaxial layers have been grown from gas sources of diethylcadmium, diisopropyltelluride and Hg vapor, as well as conventional solid sources. Optical and electrical properties are reported, demonstrating the potential of CBE for growing high quality solar cell and infrared detector material.

CdTe and HgTe surface growth kinetics for molecular and metalorganic molecular beam epitaxy

The surface growth kinetics of CdTe and HgTe have been investigated during molecular and metalorganic molecular beam epitaxy. The surface growth kinetics was studied through in-situ measurements of the growth rate as a function of flux ratio and substrate temperature on the (001), (111)B, and (211)B CdTe surface orientations. For the (001) and (111)B CdTe growth kinetics, the existence of low binding energy surface precursor sites was proposed for both molecular and atomic growth species before lattice incorporation. Intensity oscillations were observed during HgTe growth on misoriented (111)B surfaces and during CdTe growth on the (211)B orientation. The (211)B surface reconstructions displayed both vicinal and singular surface characteristics, depending on the growth flux ratio.

Growth and characterization of HgCdTe heterostructures by metalorganic molecular beam epitaxy

Abstract HgCdTe continues to be the most important semiconductor material for infrared detector applications. To date issues relating to spatial uniformity and repeatability of alloy composition have hampered the development of this technology. In this paper, we describe the growth and properties of Hg 0.72 Cd 0.28 Te epilayers and Hg 0.72 Cd 0.28 TeCdTe superlattices grown by metalorganic molecular beam epitaxy. The HgCdTe epilayers exhibited a high degree of lateral and vertical alloy composition homogeneity and also very high run-to-run uniformity. HgCdTeCdTe superlattices were also grown with a variable barrier and constant well thickness. The measured periodicity from X-ray diffraction rocking curves closely agreed with the desired values. Infrared Photoluminescence studies confirmed the high crystallinity and suggested that the luminescence was strongly excitonic with a bound exciton linewidth of 8 meV at 6 K.

MBE flexible manufacturing for HgCdTe focal plane arrays

To achieve the DoD objective of low cost high performance infrared focal plane arrays a manufacturing technique is required which is intrinsically flexible with respect to device configuration and cutoff wavelength and easily scaleable with respect to volume requirements. The approach adopted is to fully develop the technology of molecular beam epitaxy (MBE) to a level where detector array wafers with a variety of configurations can be fabricated with first pass success at a reduced cost. As a vapor phase process, MBE lends itself directly to: (1) the inclusion of real-time monitoring and process control, (2) a single or multiple wafer growth mode, (3) nearly instantaneous changes in growth parameters. A team has been assembled to carry out the program. It is composed of four industrial organizations -- Rockwell International, Hughes Aircraft Company, Texas Instruments, and Lockheed-Martin, and a university -- Georgia Tech Research Institute. Since team members are committed suppliers and users of IRFPAs, technology transfer among team members is accomplished in real-time. The technical approach has been focused on optimizing the processes necessary to fabricate p-on-n HgCdTe double layer heterostructure focal plane arrays, reducing process variance, and on documenting flexibility with respect to cutoff wavelength. Two device structures have been investigated and fabricated -- a 480 by 4 and a 128 by 128.

Recent advances in the metalorganic molecular beam epitaxy of HgCdTe

A brief review is given of recent results to assess the capability of metalorganic molecular beam epitaxy for the low-temperature growth of high-quality low-carrier-concentration CdTe and HgCdTe alloys. In particular, studies of this technique to produce highly uniform HgCdTe material and the extension of the gas source doping of CdTe and HgCdTe with ethyliodide so as to obtain back-doped electron concentrations from 1015 to 1018 cm-3 are reported. Some preliminary results on the growth of ternary CdTe/HgCdTe superlattices and the p-type doping of CdTe with As will also be presented. The electrical and optical properties of these materials were determined by resistivity and Hall effect, photoluminescence, and IR transmission measurements between 300 and 10 K.

Chemical beam epitaxy of HgCdTe

The capability of chemical beam epitaxy to address the critical material issues of the growth and doping of Hg1-xCdxTe is discussed in conjunction with its advantages for enhanced compositional and growth rate control. The potential of this technique is demonstrated from a review of the electronic and photoconductive properties of narrow-bandgap alloys (x<0.3) and preliminary studies of the n-type iodine doping of CdTe.