摘要:

A mathematical model has been developed which describes the transport phenomena and elementary reaction kinetics encountered during photoassisted organometallic vapor‐phase epitaxy of cadmium telluride. Dimethylcadmium and dimethyltellurium in helium carrier gas are fed to a horizontal, square duct containing a substrate heated to 165 °C. The organometallic compounds are photodissociated in the gas by illumination with 248 nm photons from a continuous‐wave laser. Average deposition rates predicted by the model agree to within 10% of those measured experimentally. The numerical simulations reveal that the growth rate is controlled by the photolysis rate of the organometallic compounds. This results in a linear dependence of the growth rate on dimethylcadmium pressure and laser power. The simulations further indicate that elemental tellurium deposits with cadmium telluride over a wide range of operating conditions. The elemental tellurium is avoided by operating below 20 Torr total pressure, by illuminating the gas directly above the substrate, and by feeding two–four times more dimethylcadmium than dimethyltellurium. Under these conditions, the flux of methyl radicals to the surface is sufficient to etch away the excess tellurium. The model has also been used to identify an illumination geometry suitable for obtaining uniformly thick CdTe films.

ISSN:1071-1023    

DOI:10.1116/1.585873

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

The causes for variations in quantum efficiency (QE) for boron‐implanted midwave infrared diodes formed in mercury cadmium telluride on CdTe buffered GaAs/Si substrates have been investigated. Smooth layers have QE≳30% with many of the diodes in the 50%–60% range. Layers having a faceted morphology produce diodes with QE<30%. The faceted layers have been shown by infrared absorption measurements and secondary ion mass spectrometry depth profiles to possess microinhomogeneities in composition. Carrying out comparative growths on GaAs substrates have shown that these microinhomogeneities are not due to the growth process or fundamentally due to the interdiffused multilayer process used to grow the alloy layers. A study of the origins of the faceting behavior on GaAs/Si substrates, usinginsitulaser reflectance, has shown that they form from three‐dimensional island growth, nucleating on the substrate and growing outwards to dominate the growth mode after 2 000 Å of buffer growth.

ISSN:1071-1023    

DOI:10.1116/1.585874

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

Recently, misoriented (100)GaAs or (211)GaAs substrates have been found to be favored for HgCdTe and CdTe epitaxial growths, due to low occurrence of crystalline defects. It was previously reported that both tilted (211) and (133)CdTe were grown on (211)B GaAs, like on (100)GaAs, and that (133)CdTe seemed to have better crystallinity than tilted (211)CdTe. However, these results were obtained only at substrate temperature ∼300 °C, and the occurrence of both growth orientations has not been clear yet. In this article, substrate temperature dependence of CdTe growth on (211)B GaAs substrate is studied in detail, from the view points of crystallinity and surface morphology. It turns out that these orientations can be controlled by the initial substrate temperature, i.e., tilted (211)CdTe appears at substrate temperature below 290 °C, and above 290 °C (133)CdTe can be grown. Furthermore, double‐crystal rocking curve‐full width at half‐maximum reaches 60 arcsec for (133)CdTe/(211)B GaAs. Finally, a model for the occurrence of both tilted (211) and (133) CdTe growths was qualitatively proposed.

ISSN:1071-1023    

DOI:10.1116/1.585875

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

CdTe and HgCdTe can be grown directly on Si(100) substrates by molecular‐beam epitaxy. The layers grow in the (111)B orientation. Single domain films are always obtained on Si(100) 8° off toward [011], whereas single and double domain films were obtained on nominal Si(100). A possible reason for the formation of these domains is discussed based on a microscopic model of the CdTe/Si interface. The structural quality of the layers is determined by double crystal x‐ray rocking curves. The narrowest rocking curves are obtained on single‐domain films grown on nominal Si(100) substrates; a full width at half‐maximum (FWHM) of only 230 arcsec was measured, compared to 460 arcsec on the best layer with two domains. For HgCdTe layers grown on CdTe/Si, rocking curves with 110 arcsec FWHM were measured; these layers aren‐type with electron mobilities above 5×104cm2 V−1 s−1at 23 K for a Cd mol % of 26%.

ISSN:1071-1023    

DOI:10.1116/1.585876

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

Ellipsometry is a sensitive nondestructive analytical technique well suited to the molecular‐beam epitaxy (MBE) growth process. We report its use in real time to control composition, growth rates, interdiffusion, and growth related surface defects of Cd0.2Hg0.8Te epilayers and CdTe/HgTe superlattices grown on CdTe and Cd0.96Zn0.04Te (100) substrates using a Riber 32 R&D MBE machine that has been custom modified by the manufacturer to facilitate the addition of a phase‐modulated ellipsometer. Growth rate data from ellipsometry are in good agreement with reflection high‐energy electron diffraction intensity oscillation data, double‐crystal rocking curve determinations of superlattice periodicity, and infrared transmission measurements of total thickness. The level of Hg incorporation in CdTe (100) layers is measured with ellipsometry and its temperature dependence is established. Growth‐front roughening of CdTe during the growth of CdTe/HgTe superlattices and interdiffusion between these layers on postgrowth annealing, are observed in the ellipsometric data. The results are compared with model calculations and a compositional profile of these interface structures is proposed.

ISSN:1071-1023    

DOI:10.1116/1.585877

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

Selected‐area epitaxy of CdTe grown by chemical‐beam epitaxy and migration‐enhanced epitaxy was achieved at reduced temperatures (above 225 °C) on (001) GaAs substrates patterned with SiO2. CdTe single‐crystal growth was observed on the GaAs surface while no deposition was detected on the SiO2. Selected epitaxy was further demonstrated in reduced‐area patterns with dimensions suitable for the monolithic integration of infrared focal plane and processor arrays. Growth selectivity was confirmed by scanning Auger microscopy, scanning electron microscopy, reflection high‐energy electron diffraction, and x‐ray double‐crystal rocking curve analysis. A method is proposed to reduce the growth temperature to below 200 °C; a temperature appropriate for epitaxy of device‐quality HgCdTe.

ISSN:1071-1023    

DOI:10.1116/1.585878

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

CdZnTe crystals have been grown over the full range of alloy composition by a high‐pressure Bridgman (HPB) method. Use of the inert gas over pressure reduces loss of material from the melt, and permits growth without the use of sealed ampoules, extending the range of possible alloys, and allowing a choice of crucible materials. The HPB method yields high‐quality CdZnTe and enables room‐temperature gamma radiation detectors to be made over large area wafers of undoped material for the first time.

ISSN:1071-1023    

DOI:10.1116/1.586264

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

Extensive data are presented on the arsenic doping characteristics of Hg1−xCdxTe layers grown by metalorganic chemical vapor deposition using the dopant source tertiarybutylarsine (TBAs). The incorporation of arsenic in the layer is proportional to the II–VI alkyl ratio during TBAs injection. High arsenic concentrations significantly increase the layer dislocation density. Acceptor activation efficiency (taken to be the 77 K carrier concentration divided by the layer arsenic concentration) is ∼50% for a wide range of conditions, but decreases for arsenic concentrations approaching 1018cm−3. For arsenic concentrations below low‐1017cm−3, the 77 K carrier concentration is stable even for sample annealing at 400 °C on the Te‐rich side of the phase boundary. 77 K hole mobility strongly depends on compositionx. Variable temperature Hall effect measurements show that one layer exhibits the expected carrier freeze‐out with an ionization energy of 4.8 meV, but three other layers exhibit a much smaller degree of freeze‐out. Preliminary results using the dopant source triisopropylantimony are also presented.

ISSN:1071-1023    

DOI:10.1116/1.586265

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

The influence of substrate orientation onp‐type doping was investigated on three different CdTe crystallographic orientations: (111)B, (111)A4°→(110), and (100)4°→(110). Teritarybutylarsenic was used as thep‐type dopant source in a conventional, atmospheric pressure direct alloy growth metalorganic chemical‐vapor deposition growth process. Hall measurements on annealed baseline undoped growths showed high mobility and low carrier concentration material on all three orientations. At high Hg/Te ratios, it was possible to dope the (111)B to the low 1016/cm3range and the (111)A4°→(110) and (100)4°→(110) to the low 1017/cm3range.

ISSN:1071-1023    

DOI:10.1116/1.586266

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

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 6×1016and 3×1018cm−3were obtained and showed the highest mobilities measured in epitaxialn‐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.

ISSN:1071-1023    

DOI:10.1116/1.586267

出版商:American Vacuum Society    

年代:1992

数据来源: AIP