W.R. MacEwan

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.

Optical and capacitance spectroscopy of InP:Fe

Photocapacitance, DLTS, optical absorption and photoluminescence data are presented for iron- and iron-germanium-doped Czochralski single-crystal InP. The results demonstrate that the Fe2+ to Fe+ transition is not present within the InP band gap. A feature observed in photocapacitance and optical DLTS is attributed to the presence of the Fe4+ charge state, and features associated with the well known Fe3+ and Fe2+ states also occur. Photoluminescence measurements show an iron-related band near 0.5 eV, not previously reported in the literature.

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.

Phase identification in Fe-doped GaAs single crystals

Phase analysis has been carried out on Fe-doped LEC single crystals of GaAs in order to determine the nature of the precipitates which form once the solid solubility limit of Fe in GaAs is exceeded. SEM studies have shown that a eutectic is formed in the lower parts of the crystal to solidify. LINK/EDX and magnetic measurements indicate that this eutectic consits of a previously unidentified ternary compound Fe3GaAs, and GaAs containing Fe. Magnetic measurements on the eutectic mixture and on a specially prepared sample of Fe3GaAs indicate that this new phase is ferromagnetic with a Curie temperature around 100°C.

The identification of precipitate phases in Fe-doped InP single crystals

Abstract The nature of precipitates found in Fe-doped single crystals of InP grown by the LEC method has been investigated. SEM studies show that the precipitates have only one type of morphology namely, a rhombohedral shape whilst back-scattered electron and EDAX investigations establish that a significant proportion of the precipitates are two-phase mixtures of FeP 2 and FeP. This phase analysis is confirmed by gravimetric studies. The two-phase nature of the iron-phosphide precipitation explains inconsistencies in published X-ray data for these precipitates.

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.

Residual donors in LEC indium phosphide

Abstract We report well-resolved structure in the neutral donor bound exciton “two-electron” transition photoluminescence satellites from selected relatively pure, nominally undoped single crystals of InP grown by the liquid encapsulated Czochralski (LEC) technique. This structure results from transitions at different donor species, adequately resolvable only in spectra recorded at high magnetic fields and low temperatures. Three or four donors appear. Sulphur is usually a significant species, Si is a minor donor, and an unidentified species is a principal donor which has a small negative central cell correction. These data contrast strongly with those for InP layers grown by the halide and metal organic vapour epitaxial techniques in which the dominant residual donors are S and Si, respectively.

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.

Precipitate identification in co-doped InP

Abstract The nature of precipitates found in Co-doped single crystals of InP grown by the LEC method has been investigated using scanning electron microscopy (both secondary and back scattered electrons and energy dispersive X-ray analysis (EDAX)) and Debye–Scherrer X-ray diffraction. Two phases have been detected. One has been positively identified as the cubic CoP 3 phase and was found to exist in two distinct morphologies, as cuboids at and near to the surface of the crystal and as fine rods in a eutectic CoP 3 -InP mixture within the bulk of the crystal. in some crystals another phase has been observed which is also a cobalt phosphide but significantly more Co-rich than CoP 3 . Thus far, the crystal structure of this phase has not been identified.