K. Shinohara

High‐quality GaN epitaxial layer grown by metalorganic vapor phase epitaxy on (111) MgAl2O4 substrate

We grew GaN crystals by metalorganic vapor phase epitaxy on (111) and (100) MgAl2O4 substrates. We obtained a single‐crystal GaN layer with a specular surface on the (111) substrate. The full width of half‐maximum of the x‐ray rocking curve for a 3.6 μm thick GaN layer was 310 s, comparable to the reported values for GaN on Al2O3 substrates. In the room‐temperature photoluminescence, a band‐edge emission at around 360 nm was dominant. A smooth cleaved (1100) facet of the GaN epitaxial layer was obtained, assisted by the inclined (100) cleavage of the (111) MgAl2O4 substrate. We intend this cleaved facet, which is normal to the surface, to be used as a cavity mirror in a laser diode.

Continuous operation over 1500 h of a PbTe/PbSnTe double-heterostructure laser at 77 K

Continuous operation over 1500 h at 77 K has been achieved by use of a PbTe/Pb0.93Sn0.07Te double‐heterostructure laser which was grown using the liquid‐phase‐epitaxy method. The cw threshold current changed only about 3% during the first 200 h. It is concluded that the lifetime of PbTe/PbSnTe double‐heterostructure lasers at 77 K is fundamentally very long.

Crystal growth of Hg1−xCdxTe using Te as a solvent

Abstract A method of preparing homogeneous alloy crystals of Hg 1− x Cd x Te using a zone melting procedure which employs Te as a solvent is reported. The value of x in various ingots has been measured by atomic absorption analysis and electron probe microanalysis. The results show that the compositional uniformity of cross sections of ingots was found to significantly improve by reducing the volume of the liquid zone; this caused a change from a curved to a flat solid-liquid interface

Dislocation reduction in HgCdTe epilayers on GaAs by using CdTe/CdZnTe strained-layer superlattices in CdTe layers

Abstract The structure of CdTe/CdZnTe strained layer superlattices (SLSs) which block the threading dislocations has been studied. Since the residual strain in the heteroepitaxial CdTe offsets the SLS-induced strain, SLSs located near the interface of CdTe/GaAs should be constructed with large misfit force in place. The surface dislocation density of CdTe was found to be reduced by a factor of 2.5 by using the two SLSs, and by a factor of 4.3 for four SLSs. The etch pit density of a HgCdTe layer grown on this SLS buffer layer was reduced, a beneficial side effect of reducing the dislocations in the buffer layer. Thus, strained-layer superlattices effectively block dislocations if designed properly. The dislocation density can be further reduced by increasing the number of SLSs.

Structural properties of CdTe‐ZnTe strained‐layer superlattice grown on GaAs by hot‐wall epitaxy

CdTe‐ZnTe strained‐layer superlattices (SLSs) were grown on GaAs by hot‐wall epitaxy. The individual layer thickness of the SLS is well controlled and the thickness fluctuation is less than ±1 monolayer. High‐resolution transmission electron microscopy images show coherent SLS growth. We found that two‐thirds of the threading dislocations can be reduced by inserting the SLS in CdTe/GaAs.

Oxygen striation and thermally induced microdefects in Czochralski‐grown silicon crystals

Oxygen striations in Czochralski‐grown silicon crystals have been directly observed by applying the scanning IR absorption technique to longitudinal sections. The oxygen striations were found to correlate clearly with thermally‐induced‐microdefect distributions. The results show that oxygen plays a very important role in microdefect formation. A critical oxygen concentration for microdefect introduction was estimated to be (7–8)×1017 cm−3 for 96‐h, 600 °C heat treatment.

Compositional profile of HgCdTe in metalorganic chemical vapor deposition (MOCVD) system with multinozzles

We studied the dependence of the compositional profile on the nozzle configuration in Hg1−xCdxTe growth using a metalorganic chemical vapor deposition (MOCVD) system having multinozzle injectors and a rotating susceptor in a vertical reactor. In growth, the composition depends on the concentration of dimethyl-cadmium (DMCd). In the epilayer grown by injecting DMCd from one nozzle, the x-value was highest just beneath the nozzle. The x-value peak shifts towards the rotation center when the epilayer is grown from an off-center nozzle with rotation. The compositional profile of the epilayer grown by the injection of DMCd from two nozzles was the same as the summation of the two profiles produced with one, and then the other nozzle. In a simulation based on these results, we found that 8 nozzle injectors are needed to grow the epilayer on a 3-inch substrate within a compositional variation (Δx) of 0.002.

Metalorganic chemical vapor deposition growth of CdTe on GaAs in a vertical reactor with multi-nozzles

Abstract The metalorganic chemical vapor deposition (MOCVD) growth of CdTe films on 3 inch diameter (100) GaAs substrates using a vertical rotating-susceptor reactor with linearly alligned multi-nozzles was studied. Specular single ( 1 1 1 )B CdTe films over the entire 3 inch wafer were obtained by adjusting the VI/II ratio individually for each nozzle. The thickness variation for a 2.5 μm thick CdTe films was below 8%. The full-width at half-maximum (FWHM) of the (333) double-crystal X-ray rocking curve (DCRC) was about 250 arc sec. To evaluate its suitability as a substrate for HgCdTe epilayers, a Hg0.7Cd0.3Te layer 3 μm thick was grown on the CdTe/GaAs using the same MOCVD system. The HgCdTe layer also showed a specular surface. No macroscopic crystal defects such as cellular structures or antiphase domains were observed on the etched HgCdTe surface.

Tilt growth of CdTe epilayers on sapphire substrates by MOCVD

Abstract We studied model lattice matching in the growth direction by tilt growth and found that the ratio of the tilt angle of the epilayer (α) to the offset angle of the substrate (θ) had a maximum at α / θ = 0.73, independent of the offset angle. Experimental plots of the ratio versus the full width at half maximum (FWHM) of (333) CdTe rocking curves in double-crystal X-ray diffraction show that the ratio ranges from 0.05 to 0.6 while the FWHM varies from 1100 to 400 arc sec. This result suggests that the lattice inclination orients the lattice structure perpendicular to the CdTe-sapphire heterointerface and that the tilt angle reduces defects such as dislocations and stacking faults. Most epilayers grown on sapphire substrates with offset angles above 3° were confirmed to have a α / θ ratio below 0.2. This suggests that crystal defects may be generated by shearing stress due to large offset angles. Greater defect density lowers the ratio and degrades crystallinity.

A TEM evaluation of CdTe epilayers grown on precisely oriented (111)B GaAs by hot wall epitaxy

Abstract Structural investigations, using plan-view and cross-sectional transmission electron microscopy (TEM) in addition to etch-pitting techniques, have been carried out on ( 1 1 1 )B CdTe epilayers grown on oriented ( 1 1 1 )B GaAs substrates by hot wall epitaxy (HWE). The layers are found to exhibit a complex three-dimensional twinning structure which is comprised firstly of a series of lamellar twins extending from the CdTe/GaAs interface to a height of about 6 μm in the epilayer. Above this point, lamellar twinning gives way to a six-fold pattern of single domain sectors with a twinned relationship to each other. The sectors are separated from each other by narrow, mixed domain, boundary regions with radial 〈110〉 elongations. The formation of such a twinned structure is explained in terms of epilayer curvature introduced during crystal growth as a consequence on a non-uniform gas flow distribution. In addition, grain structure in the epilayer has been investigated using Electron diffraction analysis and high resolution TEM. Although large angle grain boundaries are found at the interface, a grain regrowth mechanism leads to single crystal CdTe at the epilayer surface, at least in the single domain sectors. Grain boundaries and twin boundaries are found to accumulate in the mixed domain boundary regions. Also, long dislocation tangles are also found to be present in the mixed domain regions.