K. Kodama

New approach to the atomic layer epitaxy of GaAs using a fast gas stream

A new growth method has been developed for the atomic layer epitaxy of GaAs. The gas system was based on a conventional metalorganic vapor phase epitaxial system but the decomposition of methylgallium was suppressed in the stagnant layer by using a fast pulsed gas stream from a jet nozzle. The method enabled us to grow high purity epitaxial layers with a clear self‐limiting mechanism even at 560 °C. The variations in the growth rate with respect to various growth parameters were explained by the rate equations based on the selective adsorption of methylgallium on surface As atoms. The decomposition rate of methylgallium on the surface had an activation energy of 42 kcal/mole from 440 to 560 °C.

In situ x‐ray photoelectron spectroscopic study of GaAs grown by atomic layer epitaxy

We carried out an in situ investigation of GaAs grown by atomic layer epitaxy, using an x‐ray photoelectron spectroscopy system combined with a metalorganic vapor phase epitaxial growth chamber, where Ga(CH3)3 and AsH3 were the source gases. It has been proved that Ga(CH3)n molecules (where n=1 or 2) are decomposed into Ga atoms after being adsorbed on the GaAs surface around 500 °C. This means that the self‐limited adsorption of Ga in the atomic layer epitaxy of GaAs can be achieved on the surface where the Ga adsorbate is atomic Ga.

Carbon incorporation in GaAs layer grown by atomic layer epitaxy

Abstract The mechanism by which carbon is incorporated into GaAs layers by atomic layer epitaxy using trimethylgallium or triethylgallium was investigated. The carbon density varied from 1×10 13 to 8×10 18 cm −3 with the trimethylgallium (or triethylgallium) and arsine pulse durations and mole fractions. It was also observed that the carbon incorporation drastically changed at the pulse duration and mole fraction where the growth rate per gas cycle started to saturate to one monolayer (0.283 nm/cycle for a (100) substrate). The results were explained by the selective adsorption of carbon on surface gallium, the reaction of methygallium with arsine, and the exchange interaction between arsenic and carbon atoms. Even when the trimethylgallium source was used, the epitaxial layers grown under the optimized growth conditions exhibited an electron concentration of 1×10 14 cm −3 and a mobility of 80 000 cm 2 /V·s at 77 K, a photoluminescence spectrum with several sharp excitonic lines at the band gap energy, and an extremely low level of carbon related peaks.

Pulsed jet epitaxy of III–V compounds

An atomic layer epitaxial technique called pulsed-jet epitaxy has been developed for III–V compound crystals using metalorganic and hydride sources. The growth rate was clearly self-limited under a wide range of growth conditions. Epitaxial layers of high purity without carbon contamination could be grown. Fine patterns below 1.0μm were selectively grown with good morphology. A uniform epitaxial layer grown over a 2-inch wafer had a thickness variation within 1.0%. Strained-superlattices (GaAs)m(GaP)n were grown and exhibited an ideal self-limiting mechanism at 500°C. Structural analysis using X-ray rocking curve and Raman scattering measurements showed that superlattice growth was completely controlled within one atomic layer even for the monolayer superlattice (GaAs)1(GaP)1. Optical studies by photoluminescence and reflectance measurements suggest that the monolayer superlattice had a direct energy-band structure.

Kinetic processes in atomic‐layer epitaxy of GaAs and AlAs using a pulsed vapor‐phase method

Atomic‐layer epitaxy (ALE) has been developed for GaAs and AlAs using a pulsed vapor‐phase method using metal‐organic compounds and hydride. Growth rate has been investigated in detail as a function of various growth parameters. When arsine gas‐pulse duration is increased, the growth rate decreases drastically once a film thickness [1 monolayer (ML) for GaAs(100), (110), and (111)B, 2 ML for AlAs(100) and (111)B, and 3 ML for AlAs(110)] has been reached. A model has been suggested to explain the result.

Self-limited growth in InP epitaxy by alternate gas supply

Self-limited growth in InP epitaxy was investigated by alternately exposing the substrate to (CH3)3In(TMIn) and PH3. The growth proceeded in the atomic layer epitaxy (ALE) mode at a low temperature of 350°C. The growth rate saturated at about 0.5 monolayers (ML)/cycle, independent of the mole fractions and the exposure times of TMIn and PH3. The surface morphology and thickness uniformity were greatly improved by ALE, indicating the superiority of ALE in the fabrication of ultrathin layers and abrupt interfaces.

Atomic layer epitaxy of GaP and elucidation for self‐limiting mechanism

Atomic layer epitaxy (ALE) of GaP was performed for the first time in a low‐pressure metalorganic vapor phase epitaxial (MOVPE) reactor using trimethylgallium (TMG) and phosphine (PH3) as sources. Growth was self‐limiting for the exposure time of each reactant. X‐ray photoelectron spectroscopy (XPS) analyses were carried out to identify the adsorbates on the growth surface. There were no methyl groups on the surface Ga and the self‐limiting mechanism is due to the selective adsorption of TMG by the surface P atoms. When the substrate was exposed to a sufficient TMG flow after a submonolayer Ga was deposited by triethylgallium (TEG), growth was still self‐limiting. This supports the selective adsorption model.

Comparative study of self‐limiting growth of GaAs using different Ga‐alkyl compounds: (CH3)3Ga, C2H5(CH3)2Ga, and (C2H5)3Ga

We studied the self‐limiting growth of GaAs using three kinds of Ga‐alkyl compounds−trimethylgallium (TMGa), ethyldimethylgallium, and triethylgallium−as atomic layer epitaxy (ALE) sources. Perfect self‐limiting behavior was found only for TMGa. The self‐limiting mechanism could be explained by the surface site selectivity of the metalorganic molecules in the adsorption, desorption, and decomposition processes. We found that the degree of the site selectivity declined as methyl groups attached to a Ga atom were replaced by ethyl groups. We believe that the TMGa molecule is adsorbed without decomposition in the first step, and then fully decomposed into Ga. Three methyl groups of the adsorbed TMGa play an important role in the site selectivity and make the growth self‐limited. We studied the evolution of the chemical state of the TMGa‐exposed (001) GaAs surface by changing the length of the interruption following a TMGa pulse. There was no change in the surface chemical conditions and in the degree of self...

Selective growth of InP buried structure by chloride vapor phase epitaxy

Selective growth of an InP buried layer by In/PCl3/H2 vapor phase epitaxy was developed for buried layer GaInAsP/InP long wavelength laser diodes. For the first time, a completely flat‐surface buried layer was grown into grooves with good morphology on a (100) exactly oriented InP substrate, but not on a (100) 2° off oriented substrate. We found that the side of the groove was covered with a buried InP layer in the early stage of epitaxial growth. Therefore, the present selective growth would be effective for the protection of the interface between the active and buried layers from thermal degradation. The resistivity of InP, measured by using an n‐i‐n structure, was found to be higher than 103 Ω cm at room temperature, which is sufficient for the buried layer of an usual laser diode.

Optical investigation of MQW system InP–InGaAs–InP

A new multiquantum well system, InP–InGaAs–InP, has been grown by the chloride transport vapor phase epitaxy. The Auger measurements show that a very sharp InGaAs–InP heterointerface (less than 30 A) can be obtained by the present growth system. Optical absorption and photoluminescence measurements give the evidence for the formation of the quantum wells in InGaAs layers. Temperature dependence of photoluminescence indicates that the dominant emission at low temperatures is interpreted as the band‐to‐acceptor transition. It also shows that temperature dependence of the transition energy from hole subband to electron subband is apparently affected by the thickness of the quantum well. Two models are presented for this. One takes into account the localized phonons in the InGaAs–InP heterointerface region whose frequency is higher than that in the bulk samples. The other considers the difference in the thermal expansion coefficients of InGaAs and InP, which reduces a shift of the [000] conduction band minimu...