Photoluminescence and secondary ion mass spectrometry investigation of unintentional doping in epitaxial germanium thin films grown on III-V compound by metal-organic chemical vapor deposition

Abstract

High quality epitaxial germanium (Ge) thin films grown on lattice matched and mismatched III-V compound may lead to development of new electronic and optoelectronic devices. Understanding the doping and electronic properties of these Ge thin films is the first step in this development. In this paper, we report on high-quality epitaxial Ge thin films grown on GaAs and AlAs by metal-organic chemical vapor deposition. Cross-sectional transmission electron microscopy and atomic force microscopy reveal the high structural quality of the Ge thin films. Using photoluminescence, secondary ion mass spectrometry, and spreading resistance analysis, we investigated the unintentional doping characteristics of the fabricated Ge-on-III-V thin films. We found that arsenic (n-type doping) concentration is determined by the background partial pressure of volatile As-species (e.g., As 2 and As 4 ), which incorporate into the Ge thin films via gas phase transport during the growth. Group III element (p-type doping) incorporation in the Ge thin films occurs during the growth through a surface exchange process. There exists a trade-off between Ge film structural quality and group III element "auto-doping." III-V compound surfaces that are group III element-rich facilitate the initiation of Ge thin films with high crystalline quality and low surface roughness. However, the group-III-rich surfaces also result in high group III element (p-type doping) concentrations in the Ge thin films.

In situ grown Ge in an arsenic-free environment for GaAs/Ge/GaAs heterostructures on off-oriented (100) GaAs substrates using molecular beam epitaxy

“…Heteroepitaxy of GaAs/Ge(001) is more complex compared to Ge on (001)GaAs due to polar-on-nonpolar epitaxy. The RHEED studies indicate a basic difference in growth morphology between the growth of GaAs and that of Ge on the polar (100) surface: the growth of Ge on GaAs results in a smooth surface, [41][42][43] whereas the growth of GaAs on Ge produces a rough surface on an atomic scale as observed by several researchers. 39,55 The observed difference is explained due to an inherent difference in MBE growth mechanism between a compound semiconductor, GaAs, and an elemental semiconductor, Ge.…”

“…The PL peaks at bandgap of E g ¼ 0.783 eV, within an experimental error, corresponding to a wavelength of k ¼ 1583 nm, reveals that the electrons in C valley recombine with holes in the valence band at room temperature. 41,42 A shift of 23 nm peak as compared to relaxed Ge is observed, where the direct bandgap recombination of relaxed Ge peaks at 1550 nm. The direct radiative transition rate is about 1600 times that of the indirect transition at higher power excitation and, hence, only the direct band-to-band transition was observed in room temperature PL measurement.…”

“…Although, several groups succeeded in growing highquality Ge epitaxial layer on GaAs 19,26,27,[33][34][35][36][37][38][39][40][41][42][43] and GaAs/Ge/ GaAs heterostructures, 44,45 however, these work suffer from the interdiffusion of elements 46 and arsenic (As) contamination in the Ge layer due to the Ge and III-V material growth carried out in a single molecular beam epitaxy (MBE) chamber 34,47 or metal-organic vapor-phase epitaxy chamber. 42 This results in excess As point defects, which nucleate dislocation loops during the growth of GaAs overlayer on Ge. These loops expand during the subsequent high temperature GaAs growth to generate high threading dislocation densities in the thick GaAs film.…”

Structural, morphological, and band alignment properties of GaAs/Ge/GaAs heterostructures on (100), (110), and (111)A GaAs substrates

“…In addition, for all the three samples, Ga and As profiles show a hump at the Ge/GaAs (bottom) interface and it was due to the SIMS artifact caused by ion yield due to the change of matrix element (Ga, As, and Ge) transient effect. As pointed out by Bai et al 48 for planar Ge films at the lowest possible thickness, Ga-rich surfaces are desired; however, Ga-rich surfaces result in significant Ga exchange, resulting in high Ga concentrations in the Ge film. Interestingly, our SIMS depth profiles and the interface broadening on the (111)A GaAs surface exhibited the lowest interface broadening compared to either (100) or (110) GaAs substrates.…”

High-Q microresonators based on native germanium for precision sensing

“…For Ge grown on GaAs, the volatile arsenic background and Ga interdiffusion causes impurity incorporation, thus lowering the optical transparency in the LWIR. 29 Ge grown on Si does not suffer from such impurities, but the significant lattice mismatch between Si and Ge results in high-density threading dislocations, significantly reducing material quality. 30 To benchmark the absorption loss of Ge in the LWIR, it is necessary to exploit the performance of Ge microcavities using high-quality and low-loss material and to minimize any damage during the fabrication processes.…”