Stoichiometry Control of Compound Semiconductors

1992 ◽  
Vol 242 ◽  
Author(s):  
Jun-Ichi Nishizawa ◽  
Ken Suto ◽  
Yutaka Oyama
Keyword(s):  
Vapor Pressure ◽  
Emission Spectra ◽  
Pressure Control ◽  
Optical Microscope ◽  
Double Crystal ◽  
Temperature Growth ◽  
Bulk Crystal Growth ◽  
Group I ◽  
P Type ◽  
Stoichiometry Control

ABSTRACTVapor pressure control technology is successfully applied to the bulk crystal growth, epitaxial growth and diffusion process of ZnSe crystals. Surface morphology and the crystal quality are investigated by the optical microscope and the X-ray double crystal diffractometry as the function of the growth temperature and the applying Zn vapor pressure. The cathode luminescence is also measured to evaluate the optical properties and the effect of low temperature growth and the application of Zn vapor pressure are demonstrated, p-type ZnSe crystals are grown from the Se solution with group Ia element as a dopant under controlled Zn vapor pressure, p-n junction diodes are also prepared by the Ga diffusion from Zn solution under Se vapor pressure. Emission spectra from the p-n junction and its Zn and Se vapor pressure dependencies are also presented.

TEM and cathodoluminescence of precipitates in II-VI semiconductors

1988 ◽  
Vol 46 ◽  
pp. 488-489
Author(s):  
Joanna L. Batstone
Keyword(s):  
Crystal Growth ◽  
Band Gap ◽  
Local Strain ◽  
Wide Band ◽  
Optoelectronic Device ◽  
Wide Band Gap ◽  
Bulk Crystal Growth ◽  
Transmission Electron ◽  
Device Applications ◽  
Stoichiometry Control

Interest in II-VI semiconductors centres around optoelectronic device applications. The wide band gap II-VI semiconductors such as ZnS, ZnSe and ZnTe have been used in lasers and electroluminescent displays yielding room temperature blue luminescence. The narrow gap II-VI semiconductors such as CdTe and HgxCd1-x Te are currently used for infrared detectors, where the band gap can be varied continuously by changing the alloy composition x.Two major sources of precipitation can be identified in II-VI materials; (i) dopant introduction leading to local variations in concentration and subsequent precipitation and (ii) Te precipitation in ZnTe, CdTe and HgCdTe due to native point defects which arise from problems associated with stoichiometry control during crystal growth. Precipitation is observed in both bulk crystal growth and epitaxial growth and is frequently associated with segregation and precipitation at dislocations and grain boundaries. Precipitation has been observed using transmission electron microscopy (TEM) which is sensitive to local strain fields around inclusions.

Preparation and Properties of CdTe Films on Mo/Glass Substrates

2009 ◽  
Vol 1165 ◽  
Author(s):  
Vello Valdna ◽  
Maarja Grossberg ◽  
Hiie Jaan ◽  
Urve Kallavus ◽  
Valdek Mikli ◽  
...  
Keyword(s):  
Cadmium Chloride ◽  
Radiation Detectors ◽  
Cdte Film ◽  
Chloride Flux ◽  
Type Conductivity ◽  
Coated Glass ◽  
Glass Substrates ◽  
Group I ◽  
Cdte Films ◽  
P Type

AbstractShort-bandgap group II-VI compound cadmium telluride is widely used for the infrared optics, radiation detectors, and solar cells where p-type CdTe is needed. p-type conductivity of CdTe is mainly caused by the chlorine-based A-centers, and in part, by the less stable copper-oxygen complexes. As a rule, CdTe films are recrystallized by the help of a cadmium chloride flux that saturates CdTe with chlorine. In chlorine-saturated CdTe A-centers are converted to isoelectronic complexes that cause resistivity increasement of CdTe up to 9 orders of magnitude. Excess copper and oxygen or group I elements as sodium also deteriorate the p-type conductivity of CdTe like excess chlorine. p-type conductivity of CdTe can be restored e.g. by the vacuum annealing which removes excess chlorine from the film. Unfortunately, treatment that betters p-type conductivity of the CdTe film degrades the junction of the superstrate configuration cells. In this work we investigate possibilities to prepare p-type CdTe films on the molybdenum coated glass substrates. Samples were prepared by the vacuum evaporation and dynamic recrystallization of 6N purity CdTe on the top of Mo-coated glass substrates. Then samples were recrystallized with cadmium chloride flux under tellurium vapour pressure. Results of the test studies on the structure and electronic parameters of samples are presented and discussed.

Selective Area Deposition of Passivants, Insulators, and Epitaxial Films of II-VI Compound Semiconductors

1989 ◽  
Vol 161 ◽  
Author(s):  
D.L. Dreifus ◽  
Y. Lansari ◽  
J.W. Han ◽  
S. Hwang ◽  
J.W. Cook ◽  
...  
Keyword(s):  
Ohmic Contacts ◽  
Epitaxial Films ◽  
Semiconductor Surface ◽  
Epitaxial Layers ◽  
Double Crystal ◽  
Surface Areas ◽  
Selective Area ◽  
Lift Off ◽  
P Type ◽  
Area Deposition

ABSTRACTII-VI semiconductor surface passivants, insulators, and epitaxial films have been deposited onto selective surface areas by employing a new masking and lift-off technique. The II-VI layers were grown by either conventional or photoassisted molecular beam epitaxy (MBE). CdTe has been selectively deposited onto HgCdTe epitaxial layers as a surface passivant. Selective-area deposition of ZnS has been used in metal-insulator-semiconductor (MIS) structures. Low resistance ohmic contacts to p-type CdTe:As have also been realized through the use of selectively-placed thin films of the semi-metal HgTe followed by a thermal evaporation of In. Epitaxial layers of HgTe, HgCdTe, and HgTe-CdTe superlattices have also been grown in selective areas on CdZnTe substrates, exhibiting specular morphologies and double-crystal x-ray diffraction rocking curves (DCXD) with full widths at half maximum (FWHMs) as narrow as 140 arcseconds.

Quantum-Confined Optical Interband Transitions in 5-Doped Doping Superlattices

1989 ◽  
Vol 145 ◽  
Author(s):  
E. F. Schubert ◽  
T. D. Harris ◽  
J. E. Cunningham
Keyword(s):  
Emission Spectra ◽  
Doping Profile ◽  
Luminescence Spectra ◽  
Interband Transitions ◽  
Doping Technique ◽  
Quantum Confined ◽  
P Type ◽  
First Time ◽  
Experimental Absorption ◽  
Good Agreement

AbstractOptical absorption and photoluminescence experiments are performed on GaAs doping superlattices, which have a δ-function-like doping profile of alternating n-type and p-type dopant sheets. Absorption and emission spectra reveal for the first time the clear signature of quantum-confined interband transitions. The peaks of the experimental absorption and luminescence spectra are assigned to calculated energies of quantum-confined transitions with very good agreement. It is shown that the employment of the δ-doping technique results in improved optical properties of doping superlattices.

scholarly journals Influence of Coolant Pressure Size on Surface Roughness when Stainless Steel Machining

2019 ◽  
Vol 299 ◽  
pp. 04002
Author(s):  
Robert Cep ◽  
Lenka Cepova ◽  
Cristina Stefana Borzan ◽  
Jiri Kasal ◽  
Marek Sadilek ◽  
...  
Keyword(s):  
Surface Roughness ◽  
High Pressure ◽  
Stainless Steel ◽  
Control Valve ◽  
Pressure Control ◽  
Optical Microscope ◽  
Contact Method ◽  
External Cooling ◽  
Pressure Control Valve ◽  
Valve Housing

The paper is focused on the influence of the coolant pressure on the surface roughness of the workpiece when machining stainless steels. The components were machined on a STAR SR-32J dual spindle machining center and an external cooling unit HYTEK CHAV 160/150-AF-F-OL was used for cooling. Two stainless steel components were investigated, namely the gas control valve rod and the high-pressure control valve housing, which require low roughness Ra after machining (less than 0.375 and 0.25 micrometers respectively). The first component was tested at 8 different pressures in the range of 150 bar - 10 bar and the second component at 4 different pressures in the range of 120 bar - 10 bar. The roughness parameters were measured by the contact method using the MITUTOYO Surftest SJ-410 Roughness Tester and the Alicona InfiniteFocus optical microscope. Based on these sample input parameters, it was evaluated howmuch the pressure affects the surface quality or suggested its reduction due to the high cost of operation of the external high-pressure equipment.

On the dilatation of synthetic type Ib diamond by substitutional nitrogen impurity

1991 ◽  
Vol 337 (1648) ◽  
pp. 497-520 ◽  
Keyword(s):  
Infrared Absorption ◽  
Infrared Absorption Spectrum ◽  
Internal Standard ◽  
Optical Microscope ◽  
Lattice Parameter ◽  
Bragg Angle ◽  
Growth Sector ◽  
Double Crystal ◽  
X Ray ◽  
Nitrogen Impurity

Sequences of high Bragg-angle (0 B = 74°) double-crystal X-ray topographs taken at the SRS (Daresbury, U.K.) have yielded precise measurements of lattice parameter differences between growth sectors of different crystallographic forms in a large undoped synthetic diamond whose type Ib infrared absorption spectrum (principal peak at 1130 cm -1 ) indicated atomically dispersed nitrogen, singly substituting for carbon, as the only detectable impurity. The plate-shaped specimen, polished parallel to (110), 5.0 x 3.2 mm 2 in area, 0.7 mm thick, possessed an unusually well developed (110) growth sector containing nitrogen impurity concentration of only ca. 10 -6 , which served as an internal standard of pure-diamond lattice parameter with which lattice parameters of nitrogen-containing growth sectors were compared. The specimen’s suitability for precision diffractometry was checked by comprehensive tests using optical microscope techniques, cathodoluminescence and single-crystal X-ray topography. The double-crystal combination was silicon reference crystal, asymmetric 175 reflection, with diamond specimen symmetrical 440 reflection. The principal measurement was the increase of the lattice parameter, a 0 , of the (111) growth sector (nitrogen content 88 + 7 parts per 10 6 atomic) relative to that of the (110) sector: Aa 0 / a 0 = 1.18 + 0.07 x 10 -5 . In terms of measured infrared absorption coefficient at 1130 cm -1 , this gives Aa 0/a 0 = (2.95 + 0.27) x 10 -6 [p(1130 cm -1 )/cm -1 ], which is believed to hold for growth sectors of all crystallographic forms. Combination with the nitrogen assay findings of Woods, van Wyk & Collins ( Phil. Mag. B 62. 589-595 (1990)) provides a direct relation to c N , the fractional atomic concentration of substitutional nitrogen, as A a 0 / a 0 = (0.14 + 0.02) c N , which indicates that the effective volume of a single substitutional nitrogen atom in diamond is 1.41 +0.06 times that of the carbon atom it replaces. This substantial dilatation conflicts with several models for the substitutional nitrogen structure.

Fermi Level Inhomogeneities on GaAs(110) Surface Imaged with a Photoelectron Microscope

1992 ◽  
Vol 260 ◽  
Author(s):  
Changyoung Kim ◽  
Paul L. King ◽  
Piero Pianetta
Keyword(s):  
Fermi Level ◽  
Optical Microscope ◽  
Level Energy ◽  
Band Bending ◽  
Highly Correlated ◽  
P Type ◽  
Low Coverage ◽  
Lateral Variations ◽  
Surface Fermi Level ◽  
Better Than

ABSTRACTA photoelectron microscope operating with a retarding field analyzer has been used to exploit core level energy shifts due to band bending in order to directly image Fermi level variations on n- and p-type cleaved GaAs(110) surfaces. Fermi level maps resolved to better than 10 um indicate lateral variations in the surface Fermi level which are often quite abrupt. In agreement with earlier, lower resolution work [1], Fermi level topography is found to be highly correlated with surface roughness as characterized by SEM, optical microscope and stylus profi lometer. The largest defect derived pinnings encountered to date resut in the Fermi level lying 0.5 eV above the VBM for both n- and p-type GaAs. Low coverage In evaporations have the. effect of reducing Fermi level contrast as Fermi levels in formerly unpinned regions move into the gap.

THz Emission from SiC Natural Superlattice Diodes Induced by Strong Electrical Field

2018 ◽  
Vol 924 ◽  
pp. 310-313 ◽  
Author(s):  
Vladimir Ilich Sankin ◽  
Alexander V. Andrianov ◽  
A.G. Petrov ◽  
A.O. Zachar'in ◽  
Sergey S. Nagalyuk ◽  
...  
Keyword(s):  
High Resistance ◽  
Emission Spectra ◽  
Negative Differential Conductivity ◽  
Differential Conductivity ◽  
Bloch Oscillations ◽  
Electrical Field ◽  
Type Conductivity ◽  
Natural Superlattice ◽  
P Type

Recently the intense terahertz electroluminescence from monopolar n++–n– –n+ structures of 6H- and 8H-SiC of natural superlattices at helium temperatures due to Bloch oscillations was discovered. In the present work we present the THz emission spectra of bipolar n++–π–n+ structures (π is a high-resistance layer of p-type conductivity) of natural superlattices 4H-, 8H- and 15R-SiC at 7 K. The bipolar n++–π–n+ structures of 4H- and 8H-SiC were analogous to those of structures for which the negative differential conductivity effect was observed earlier for three polytypes (4H, 6H and 8H) at T=300 K. We demonstrate resemblance and differences of the spontaneous THz emission spectra for the monopolar and bipolar 4H-, 6H- 8H- and 15R-SiC natural superlattices caused by Bloch oscillations of electrons in the SiC natural superlattice.

GaAs epitaxial layers obtained by close-spaced vapor transport in H2 + H2O and H2 + CO2 ambients: Fine control of the growth rate and its effect on the electrical properties of the layers

1994 ◽  
Vol 72 (1-2) ◽  
pp. 44-50
Author(s):  
D. Cossement ◽  
Z. Huang ◽  
G. Perron ◽  
B. Jean ◽  
J. P. Dodelet
Keyword(s):  
Growth Rate ◽  
Water Vapor ◽  
Vapor Pressure ◽  
Water Vapor Pressure ◽  
Vapor Transport ◽  
Epitaxial Layers ◽  
Fine Control ◽  
Experimental Values ◽  
P Type

In view of developing the close-spaced vapor transport technique (CSVT) to obtain III/V homojunction solar cells, it is necessary to finely control the growth rate of GaAs epitaxial layers. This has been performed either by controlling the water vapor pressure, [Formula: see text] injected in the reactor along with H2, in H2 + H2O ambient, or by controlling the water vapor pressure generated in situ by the reaction of H2 + CO2 in the reactor. For H2 + CO2 ambient, [Formula: see text], controls [Formula: see text] according to the following reaction: [Formula: see text]. The growth rates calculated with a diffusion controlled model are in agreement with the experimental values for both ambients, including the observation of a maximum in the evolution of the growth rate with [Formula: see text], Controlling the growth rate of GaAs by changing [Formula: see text] affects the carrier density (NA–ND) of p-type layers grown from Zn-doped GaAs sources. In both ambients (NA–ND) is a function of [Formula: see text]. Such a behavior is also obtained for the calculated carrier densities. It is the result of the transport of Zn as ZnO in CSVT. In H2 + CO2 ambient, where H2O and C are generated in situ, carbon is not incorporated as a major p-type doping impurity, contrarily to expectations, n-type GaAs layers were also obtained from Te-doped GaAs sources. In that case, the measured NA–ND values are not affected by changes in [Formula: see text] because water is not involved in the transport of Te in CSVT.

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