G.J. Davies

Arsenic stabilization of InP substrates for growth of GaxIn1−xAs layers by molecular beam epitaxy

A new method of cleaning InP substrates under molecular beam epitaxy conditions involving heating to ⩾500 °C in an As4 flux (JAs4 ≃1015–1016 cm−2 s−1) is described. Evidence of surface cleanliness, good morphology, ordered surface reconstruction, and integrity of chemical composition at the interface is given. Lattice‐matched layers of Ga0.47In0.53As grown on InP substrates cleaned in this way showed excellent electrical properties: e.g. a room‐temperature mobility μ300=8600 cmPu2 V−1 s−1 at n300 =1016 cm−3.

Surface chemical processes in metal organic molecular‐beam epitaxy; Ga deposition from triethylgallium on GaAs(100)

The adsorption of triethylgallium on the GaAs (100) (4×1) surface has been studied using the techniques of low energy electron diffraction, x‐ray photoelectron and Auger spectroscopies, high resolution electron energy loss spectroscopy and temperature‐programmed desorption. Condensed multilayers of the organometallic compound formed following adsorption at 150 K desorb from the surface at ∼170 K to leave a chemisorbed molecular monolayer of triethylgallium. Upon further heating this layer partially desorbs and partially decomposes to form diethylgallium in two competing processes. The diethylgallium so formed can also desorb or otherwise decompose ultimately to adsorbed Ga atoms in a reaction which results in the formation of hydrogen, ethene, and ethane. The temperature‐programmed desorption characteristics of these latter species are found to be similar to those observed for a dissociated layer of ethyl bromide. A reaction scheme is proposed to account for the observations and kinetic parameters are obt...

Selective area growth for opto-electronic integrated circuits (OEICs)

Abstract Selective area epitaxy (SAE) is emerging as an important technology in the fabrication of optoelectronic integrated circuits. This paper reviews the current growth technologies for their applicability to the process of SAE. It discusses in detail the interaction on the masked area with the adjoining epitaxial window. The minimization of the features formed by this interaction whilst optimizing selectivity is seen as the main aim of the growth processes.

Selective area growth of InP/InGaAs multiple quantum well laser structures by metalorganic molecular beam epitaxy

Selective area growth of InP/InGaAs multiple quantum well laser structures has been demonstrated in openings defined in Si3 N4 layers on InP substrates. Growth was achieved, by metalorganic molecular beam epitaxy, in openings as small as 3 μm wide, but no growth occurred on the dielectric coating. Cathodoluminescence from individual laser stripes was observed at 300 K with a wavelength determined to be 1.57 μm and at 100 K with a wavelength of 1.46 μm.

Growth and MBMS studies of reaction mechanisms for InxGa1−xAs CBE

Abstract The reaction mechanism involved in the growth of In x Ga 1− x As lattice matched to InP by chemical beam epitaxy (CBE) was investigated using growth and modulated beam mass spectrometry studies. Emphasis was placed on elucidating how variations in substrate temperature, indium composition and arsenic overpressure influence growth kinetics and how sensitive changes in experimental conditions bring about deviations in the ideal stoichiometry (In 0.53 Ga 0.47 As) required for lattice matching to InP. Our observations indicate that the compositional variations in the InGaAs stoichiometry at high temperatures (> 485°C) arise because of the changes in the DEG decomposition: desorption branching ratio which is controlled by a temperature- and arsenic pressure-dependent surface population of indium atoms. The low temperature behaviour is governed by the availability of metal surface sites for triethylgallium decomposition which is increased by the presence of surface indium atoms.

Surface studies of the thermal decomposition of triethylgallium on GaAs (100)

Abstract The adsorption and surface decomposition of triethylgallium (TEG) on GaAs (100) has been studied using XPS and thermal desorption techniques. TEG is found to adsorb in a molecular form on the Ga rich (4×1) surface below 150 K. As the surface temperature is raised, this molecular state dissociates to form Ga and adsorbed ethyl species. The overall cracking reaction occurs in competition with the desorption of TEG and diethylgallium (DEG). Under the conditions of our experiments the adsorbed ethyl species formed above are found to dissociate above 600 K to form mainly gas phase ethene and hydrogen with traces of ethane, resulting in the formation of a pure Ga layer within the sensitivity limits imposed by XPS.

Anomalous silicon and tin doping behaviour in indium phosphide grown by chemical beam epitaxy

Abstract Anomalous behaviour of the most commonly used n-type dopants, Si and Sn, has been observed in the growth of InP by chemical beam epitaxy. For Si, the doping level is found to decrease with time. It is postulated that this is due to the formation of carbon and silicon carbide deposits in the dopant cell. The behaviour of Sn is more complex. For Sn cell temperatures in the range 600–750°C incorporation is proportional to the Sn vapour pressure. However, at low temperatures, 175–350°C, anomalously large incorporations of Sn are observed. This behaviour is attributed to the formation of a volatile metalorganic species within the Sn cell.

Applications of MBMS and surface spectroscopic techniques in the study of reaction mechanisms in CBE; investigations of the reactivity of tritertiarybutylgallium and triisobutylgallium as alternative precursors for epilayer growth

Abstract Current approaches to the study of reaction mechanisms in CBE and investigations of the potential of triisobutylgallium and tritertiarybutylgallium as novel CBE precursors are reviewed. Surface spectroscopic techniques indicate that adsorbed iso-butyl radicals decompose to produce gaseous butene and hydrogen at significantly lower temperatures than in the corresponding process for ethyl radicals on GaAs, resulting in lowered growth temperatures and low temperature C incorporation levels in comparison to the results obtained with triethylgallium. A β-methyl migration occurs at higher temperatures causing C to deposit irreversibly on the surface in the presence of Al. Lowered temperatures for the β-hydride elimination reaction are also observed for adsorbed tertiarybutyl radicals and the absence of β-methyl groups avoids the facile C deposition process seen for iso-butyl. These potential advantages associated with tertiarybutyl ligands cannot be realized straightforwardly in CBE using tritertiarybutylgallium however, since steric crowding effects result in the inefficient total dissociation of the adsorbing precursor molecule.

Electrochemical sulfur doping of GaAs grown by molecular beam epitaxy

A novel method of intentionally doping molecular beam epitaxy grown GaAs n‐ type is described. The donor atoms are sulfur, from a beam of S2, generated in a low temperature (200 °C), electrochemical Knudsen cell. The galvanic cell is Pt/Ag/AgI/Ag2S/Pt, where the flow of current through the cell, with the positive pole at the Ag2S is a measure of the sulfur flux effusing from the cell. Net carrier concentrations n between ∼1015 and ∼1018 cm−3 have been obtained. There is no detectable accumulation of S at the surface for high donor concentrations (∼1018 cm−3) in the bulk. This novel method of sulfur generation has a particularly fast (<1 sec) response time—much faster than the thermal equilibration times of conventional thermal Knudsen sources. Complicated doping profiles are shown to be produced relatively easily with a single doping source using this technique. Free‐electron mobilities μ300 K = 6000 cm2/V sec and μ77 K = 17 000 cm2/V sec have been obtained for sulfur doped layers with n = 1.1016 cm−3.

The influence of growth conditions on the growth rate and composition of GaAs and GaInAs alloys grown by chemical beam epitaxy

We have studied the effect of source species, substrate temperature, substrate orientation, and group‐V overpressure on the growth rate and composition of GaAs and InGaAs alloys grown by chemical beam epitaxy. Our results for GaAs growth rate versus substrate temperature show a significant effect of group‐V overpressure on the details of this dependence. The incorporation of gallium from triethylgallium into GaInAs alloys is found to be strongly dependent on temperature and alloy indium concentration, but independent of the source of indium. It is also significantly dependent on group‐V overpressure. We could find no effect on growth rate or composition dependence between growth on nominally (100) GaAs and InP substrates, and those cut 2° or 3° off axis.