Chloride Atomic Layer Epitaxy Research Articles

Theoretical studies on the chloride ALE process

Ab initio molecular orbital calculations were performed to systematically investigate the chloride atomic layer epitaxy (ALE) process of GaAs. In the Ga layer formation, the GaCl molecule as a source is first adsorbed onto the As dangling-bond (DB) site through electronic “configuration mixing”. Consequently, the ambient H 2 reactively eliminates the Cl atom as HCl, where the “electron delocalization” is the driving factor of reaction. As layer formation via As 2 adsorption onto the Ga-DB site was also investigated. The results show that the π orbitals of As 2 are used to form the As-Ga bonds through “configuration mixing”, as in the case of GaCl/As-DB. The calculated energetics are consistent with the experimental data.

Theoretical study of the Cl desorption reaction induced by H 2 in the chloride atomic layer epitaxy

The chloride ALE (atomic layer epitaxy) technique is now common to grow GaAs crystals, where the GaCl molecule is used to supply Ga atoms for the As dangling bond site. The present ab initio molecular orbital calculations predict that Cl atoms are desorbed as HCl by the single-site reaction which is induced by H 2. The reaction scheme is represented as > GaCl + H 2 → > GaH + HCl, which is driven by the concerted electron delocalizations among those four atoms. It is shown that the reaction is endothermic by the amount of 30 kcal/mol and occurs through the four-centred transition state of “late-barrier” type. The activation energy is estimated to be 37–44 kcal/mol, which agrees well with the experimental value of 40–50 kcal/mol.

In situ optical characterization of GaAs and InP surfaces during chloride atomic layer epitaxy

In this paper, the results of in situ surface photo-absorption (SPA) measurements on GaAs and InP surfaces under an alternating supply of GaCl and AsH 3 or InCl and tertialybutylphosphine (TBP) in chloride atomic layer epitaxy (ALE) are presented. It was found that the reflection intensity varied by several per cent, depending on the source gas supply sequence. This reflection intensity was constant during the GaCl and InCl supply from both the GaAs and InP surfaces, probably corresponding to the self-limiting mechanism of chloride ALE. Reflection spectra from a GaAs surface during and after GaCl supply were found to be similar. They showed anisotropic spectral structures according to the incidence azimuth of light. This anisotropy is considered to originate from the existence of surface dimers. Thus, a GaAs surface under GaCl supply is assumed to be covered by Ga. In contrast, the spectra from an InP surface during InCl supply were isotropic and different from the anisotropic spectra measured from an In-stabilized surface formed by P desorption. Accordingly, it is assumed the Cl adsorbs on an InP surface during InCl supply and prevents the formation of dimers. The different behavior of Cl on GaAs and InP may be due to a different reaction rate with H 2.

Study of self-limiting growth mechanism in chloride ALE

The growth process of chloride atomic layer epitaxy (ALE) using GaCl is studied using the temperature programmed desorption method (TPD), the surface photo-absorption (SPA) method and ab initio molecular orbital calculations. From the TPD measurements, the GaCl adsorption energy is calculated to be 32 kcal mol -1 and 38 kcal mol -1 for Ga-terminated and As-terminated surfaces respectively. In the absence of H 2, the Ga-Cl bond appears to be very stable in the adsorption state. Process simulation using a simple cluster model of (AsH 2) 2-GaCl indicates that adsorption is completed by forming σ and π covalent bonds, and that there is hardly any self-dissociation of the Ga-Cl bond. From SPA measurements in the ALE system with ambient H 2, a strong similarity is found between the spectra of the GaCl-supplying surface and the Ga-covered surface. Based on these results, a model of the chemical process in chloride ALE is proposed where adsorbed GaCl molecules can react immediately with hydrogen and Cl is released from the surface as HCl. A self-limiting mechanism results from the very short residence time of GaCl (∼ 10 -3s at 450 °C) on the Ga-terminated surface.

特集「結晶成長表面の“光プローブ”による評価」 ＧａＡｓおよびＩｎＰクロライド原子層エピタキシーにおけるブリュースター角入射表面光吸収法（ＳＰＡ）による表面“その場”観察

特集「結晶成長表面の“光プローブ”による評価」 ＧａＡｓおよびＩｎＰクロライド原子層エピタキシーにおけるブリュースター角入射表面光吸収法（ＳＰＡ）による表面“その場”観察

In situ optical characterization of GaAs surfaces under alternating supply of GaCl and AsH3

This letter describes the use of surface photoabsorption (SPA) measurements to characterize GaAs substrate surfaces under an alternating supply of GaCl and AsH3 in chloride atomic layer epitaxy (ALE). This characterization technique utilizes p-polarized light incident at the Brewster angle, which virtually eliminates the bulk contribution of the reflected light. It was found that the reflection intensity varied by several percent depending on the source gas supply sequence. This reflection intensity was constant during continuous GaCl supply, which corresponded to the self-limiting mechanism of chloride ALE. Optical reflection spectra were measured in the range of 300–800 nm during the flow of each source gas. The normalized spectra of reflection difference between GaCl and AsH3 supply depended on the incidence azimuth, which showed the existence of anisotropic surface bonds. By comparing these spectra to the reference data using triethylgallium as a Ga source, the GaAs surface under GaCl exposure was assumed to be a Ga-stabilized surface at 520 °C.

Atomic layer epitaxy of III-V compounds: chemistry and applications

Atomic layer epitaxy (ALE) of III-V compounds is addressed, with particular focus on ALE by chloride source gases of group III elements and hybrids of group V elements. A self-limiting growth mechanism in ALE is the most significant advantage over other epitaxial methods. To realize this mechanism, selections of source gases and the reactor gases and the reactor design are described. The chemistry and growth kinetics of ALE, which also provide interesting information for understanding other vapor phase epitaxy (VPE) processes, are discussed, and a model of the self-limiting growth mechanism for chloride ALE is proposed. As a promising application of ALE, the growth of fine structures using sidewall epitaxy and selective area growth is demonstrated. Prospects for the future are briefly discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Temperature programmed desorption study of gallium chloride adsorbed on GaAs surfaces

Adsorption of gallium chloride (GaCl) on GaAs (100), (111)A and (111)B surfaces is studied by temperature programmed desorption (TPD). A GaCl molecular beam is produced by a newly designed GaCl cell. TPD measurements are carried out for (100) 2×4, (100) 4×6, (111)B √19×√19 and (111)A 2×2 reconstructed surfaces. GaCl desorption is observed from these surfaces, while the desorption of GaCl x ( x=2, 3), AsCl x ( x=1≁3) and Cl 2 is not detected. Two GaCl peaks appear at 220 and 330°C for (100) 2×4, 4×6 and (111)A 2×2 surfaces, and a single peak appears at 330°C for the (111)B surface. The GaCl peaks at 220 and 330°C are assigned to the adsorption on Ga and As sites, respectively. The adsorption energy of GaCl is calculated to be 38 kcal/mol for the As sites and 32 kcal/mol for the Ga sites. The self-limiting process in chloride atomic layer epitaxy (ALE) is discussed.

InGaP/GaAs single quantum well structure growth on GaAs facet walls by chloride atomic layer epitaxy

InGaP/GaAs single quantum well(SQW) structure growth on GaAs facet wall is achieved by atomic layer epitaxy (ALE) using chloride source gases, such as InCl and GaCl. GaAs facets are formed on GaAs(100) surface openings by conventional hydride vapor phase epitaxy, which have {011} sidewalls perpendicular to the surface, {111}B and (100) faces. ALE growth of SQWs onto these faces results in a very smooth and uniform surface, as shown by scanning electron microscopy observation and cathodoluminescence measurements. The self-limiting mechanism for ALE is also retained in such selective sidewall growth of heterostructures.

InAs and InGaAs Growth by Chloride Atomic Layer Epitaxy

AbstractInAs chloride ALE has been carried out in detail, resulting in successful InGaAs ALE on (111)B InP substrates. InAs growth of 0.9 ML/cycle is obtained for (111)B InAs substrates at temperatures below 375 °C, while growth rates for (100) and (111)A substrates steadily decrease with increases in growth temperature. The growth rates are independent of InCI pressure at 375 °C, suggesting a self-limiting growth factor in InAs chloride ALE. (GaAs)1(InAs)1 and (GaAs)2(InAs)2 superalloys can be prepared on (111)B InP substrates at 375 °C. Growth rates and crystal compositions for both layers agree well with the values expected for ideal superalloys. The presence of superlattice structures is indicated by X-ray diffraction measurement,