G.T. Brown

The growth of dislocation-free Ge-DOPED InP

Abstract It is shown that the dislocation density of single crystals of InP grown by the liquid encapsulation Czochralski technique can be modified by doping the crystals with germanium and that at germanium concentrations in excess of 10 19 atoms cm -3 , dislocation-free material can be produced. The structural quality of such material, as assessed by chemical etching, X-ray topography and high voltage electron microscopy is also discussed. It is further shown that at a slightly lower doping level, 10 18 atoms cm -3 , dislocation- free material can be produced at small crystal diameters.

Photo-stimulated II–VI crystal growth: A study of low temperature epitaxy

Abstract A comparison is made with low temperature epitaxial growth of II–VI compounds using photo-MOVPE and alternatives such as MBE and pyrolytic MOVPE. A major attraction for photo-MOVPE is the potential for selective area deposition which could work in the substrate range of 200 to 300°C. However, at temperatures below 200°C, the growth rates are low ( ≈0.1 μm/h) and in this paper reasons for this are sought. The growth rate of HgTe decreases with an activation energy of 24.3 kcal/mol, however, with increased UV intensity the low temperature growth rate could be enhanced. CdTe photo-MOVPE growth rates are reduced at low temperatures to avoid the onset of homogeneous CdTe formation. This process has been modelled and can explain experimental conditions of growth rate and temperature where epitaxial growth will occur. The quality of epitaxial layers has been assessed by double crystal X-ray diffraction. HgTe layers are of very high quality and rocking curve widths approximately two times the theoretical half width have been measured. CdTe and CMT layers are more variable and an unusual feature of tilt for homo-epitaxy has been seen. However, the best CdTe layers had rocking curve widths within a factor of two of theoretical and were similar in quality to HgTe photo-MOVPE.

Dislocation clusters in Czochralski-grown single crystal indium phosphide

Abstract Clusters of etch pits which sometimes form in single crystal indium phosphide grown by the Czochralski liquid-encapsulation technique, are shown to equate with prismatic dislocation loops generated by a stress source at the centre of the cluster. The morphology of the clusters and the conditions under which such clusters form are shown to be consistent with the presence of either a precipitate or an inclusion. It is demonstrated that water vapour associated with the boric oxide used as the liquid encapsulant is a positive cause of clusters and that vacuum baking is a pre-requisite for their control. The elements responsible for the stress generation promoting the clusters have not been positively identified but the likely possibilities are discussed.

Effect of growth temperature on the optical, electrical and crystallographic properties of epitaxial indium gallium arsenide grown by MOCVD in an atmospheric pressure reactor

Indium gallium arsenide was grown epitaxially by metalorganic chemical vapour deposition (MOCVD) on (100) indium phosphide using trimethylindium. At an optimum growth temperature of 680°C, material of very good properties can be grown. The carrier concentration is 1x1015 cm-3 n-type with a mobility 80000 cm2 s-1 V-1 at 7 K. Double crystal X-ray diffraction rocking curve widths are <30 arc seconds using the (400) reflection with Cu radiation and the non-dispersive mode. The peak width in photoluminescence spectra at 2 K is < 2 meV. At lower growth temperatures the photoluminescence deteriorates dramatically. In previous work this has been attributed to enhanced carbon incorporation. In this work X-ray diffraction and transmission electron microscopy (TEM) measurements indicate that the deterioration is structural in origin and possibly due to the onset of longwavelength spinodal decomposition. TEM studies show that the interface between alloy and substrate is essentially defect free for optimally grown near lattice matched layers. Interfaces showing 2D electron gas effects and quantum wells can readily be grown. For wells, pauses in the growth can be used to sharpen interfaces and produce quantum wells of high photoluminescence efficiency.

The growth and perfection of single crystal indium phosphide produced by the LEC technique

Abstract This paper describes recent studies at RSRE concerned with identifying residual impurities and structural defects in single crystal InP grown by the Czochralski liquid encapsulation technique (LEC) and discusses means whereby the impurities and defects can be controlled. The role of some deliberately added dopants (e.g., Fe, Co and Ge) in inducing specific properties is also described.

The Czochralski growth of gallium antimonide single crystals under reducing conditions

Abstract It is shown that the surface film which often impairs seeding and crystal growth from gallium antimonide melts can be controlled without the need for a scavenging encapsulant by treating the melt with high purity hydrogen prior to and during growth. Melts treated thus can be seeded directly and permit the growth of twin-free single crystals by the Czochralski technique. The chemical, electrical and structural characteristics of such crystals are also discussed.

The single crystal growth and electrical properties of cobalt-doped indium phosphide

It is shown that semi-insulating properties can be induced in single crystals of indium phosphide grown by the liquid encapsulation Czochralski technique by using cobalt as a dopant. A mean value of segregation coefficient for cobalt in InP equal to 4 × 10−5 has been determined. Precipitation of a phosphide of cobalt is shown to limit the yield of useful semi-insulating material at high cobalt concentrations. The onset of semi-insulating behaviour occurs at a cobalt concentration in the crystal which equates approximately to the residual background concentration of n-type carriers. The close analogy of this behaviour with that observed in iron-doped crystals suggests that the semi-insulating properties are derived from Co2+ energy states which are shown to be present in these cobalt-doped crystals.

Interfacial studies and electrical characterisation of heteroepitaxial InSb on GaAs (100) grown by MBE

The growth by molecular beam epitaxy of InSb layers (0.5 < t < 10 μm) on undoped GaAs (100) substrates has been undertaken. In situ reflection high energy electron diffraction and Auger electron spectroscopy have been used to investigate the initial stages of InSb layer nucleation. The GaAs/InSb interface has also been investigated ex vacuo using transmission electron microscopy and secondary ion mass spectrometry. The data reveal a maximum interface width of 25 nm and indicate that the large mismatch (14.6% at room temperature) is accommodated by a network of misfit dislocations at the epilayer substrate interface. Nevertheless, transmission electron microscopy studies and data obtained from double crystal X-ray rocking curves show that the structural quality of the heteroepitaxial InSb improves considerably with increasing layer thickness. The electrical and morphological properties of the InSb heteroepitaxial layers have also been assessed using 77 K Hall, 2 K photoluminescence and Nomarski optical interference microscopy. All layers grown have exhibited p-type carrier concentrations (p ∽ 2 x 1015 cm-3), a value somewhat higher than observed for the corresponding homoepitaxial material.

Control of dislocation structures in LEC single crystal InP

Abstract It is shown here that formation of the major dislocation structures detected in single crystal InP, such as clusters and large rectangular prismatic loops, can be prevented during LEC growth. The conditions under which this control can be applied are entirely compatible with the techniques used to inhibit dislocation formation both by slip and the propagation of dislocations from the seed. In consequence, InP crystals with very low dislocation densities can now be produced.

A study of layer composition of InGaAs/InP multiquantum wells grown by metalorganic chemical vapor deposition using double‐crystal x‐ray diffraction theory and experiment

InGaAs/InP multiquantum wells grown by metalorganic chemical vapor deposition have been studied by fitting computer simulated theoretical double‐crystal x‐ray rocking curves to experimental data. It is shown that the technique can identify the carry over of As into the InP barriers and the concentration and distribution of As are determined. The highest concentration of As observed was 21%, which was confined to the first 50 A of the barrier and fell to 2% towards the following interface. Both the maximum and minimum concentration of As was found to decrease as a function of the pause time between growth of the InGaAs quantum well and the InP barrier layers. These observations were confirmed by secondary ion mass spectrometry (SIMS) and other experimental data on the same material is shown to support the results.