A Scanning Tunneling Microscopy-Reflection High Energy Electron Diffraction-Rate Equation Study of the Molecular Beam Epitaxial Growth of InAs on GaAs(001), (110) and (111)A–Quantum Dots and Two-Dimensional Modes

Abstract

The growth modes of InAs on the three low index orientations of GaAs during molecular beam epitaxy (MBE) are very different, despite a constant lattice mismatch of ≈7%. Coherent three-dimensional (3D) growth occurs only on (001) surfaces; on the other two orientations strain relaxation involves misfit dislocation formation and a continuous two dimensional growth mode. Strain is therefore not a sufficient condition to induce 3D growth. Reflection high-energy electron-diffraction and scanning tunnelling microscopy observations confirm that an intermediate `wetting layer' is formed on (001)-oriented substrates prior to the formation of quantum dots. The thickness and composition of this layer is dependent on both growth temperature and the amount of InAs deposited, but it is always an (In, Ga)As alloy. We have also confirmed that substantial mass transport occurs during quantum dot formation and that the dots themselves have an alloy composition. A model to account for at least some of these effects, based on rate equations, is introduced.

Recent Progress in Computational Materials Science for Semiconductor Epitaxial Growth

“…The (2 × 2) with TAs is stabilized only at low temperatures, while the (2 × 2) with VIn appears at high temperatures. The stable temperature ranges for the (2 × 2) with VIn (beyond 550-600 K) on the InAs(111)-WL are consistent with MBE growth temperature range of 723-773 K (black area) at which the (2 × 2) with VIn is observed experimentally [20,35,36]. It should be noted that the InAs(111)-WL with As-adatom surface newly appears between stable regions of the (2 × 2) with VIn and the (2 × 2) with TAs, where the As adatom stably resides in the interstitial site bonding with three substrate In atoms.…”

“…The As-adatom surface makes up this deficiency in charge density, where the charge density around the As adatom is transferred to the substrate In atom to strengthen the interatomic bond between the In and As atoms. Therefore, the As-adatom surface appears as a stable phase between V In and T As on the InAs (111) [20,35,36]. It should be noted that the InAs(111)-WL with As-adatom surface newly appears between stable regions of the (2 × 2) with VIn and the (2 × 2) with TAs, where the As adatom stably resides in the interstitial site bonding with three substrate In atoms.…”

“…Many studies have been done to investigate the InAs/GaAs growth using reflection high-energy electron-diffraction (RHEED) and scanning tunneling microscopy (STM). Joyce et al [20] found that an intermediate wetting layer (WL) is formed on the (001)-oriented substrates prior to the formation of QDs while strain relaxation involving misfit dislocation formation causes a continuous 2D growth mode on the (111)A. For the InAs/GaAs(111), Yamaguchi et al [21] reported experimental measurements using STM on the mechanisms of strain relaxation in InAs/GaAs(111)A hetero-epitaxy to propose a possible model for the resulting semicoherent interface structure.…”

“…Figure 13 also includes the boundary denoted by dotted line for the InAs/GaAs(110) with E d = 0.96 (eV/Å) obtained by ab initio calculations [14]. The InAs/GaAs(110) system has been extensively examined using RHEED, TEM, and STM for a wide range of film thickness where the growth follows a layer-by-layer mode irrespective of thickness and strain relaxation occurs solely by the formation of MD [20,56]. However, self-assembled InAs QD has been realized on GaAs(110) using MBE with buffer layer insertion [57] and MOVPE with optimizing growth temperature [58], where the strain reduction is considered to be a crucial origin of the QD formation.…”

Theoretical Investigations for Strain Relaxation and Growth Mode of InAs Thin layers on GaAs(111)A

“…Due to the 7% lattice mismatch between InAs and GaAs, the InAs on the GaAs(001) produces three-dimensional (3D) QDs with Stranski-Krastanov (SK) growth mode [1]. Despite a constant lattice mismatch, the InAs on the GaAs(111)A with Ga topmost layer exhibits two-dimensional (2D) growth with the misfit dislocation (MD) formation [2,3]. Although many studies have been done investigating the QD formation on the InAs/GaAs(001) [4][5][6][7][8][9][10][11][12], there have been only a few studies of the relationship between strain relaxation and the 2D growth on the InAs/GaAs(111)A [3,13,14].…”