Low-temperature photoluminescence study of thin epitaxial GaAs films on Ge substrates

Abstract

Thin epitaxial GaAs films, with thickness varying from 140 to 1000 nm and different Si doping levels, were grown at 650°C by organometallic vapor phase epitaxy (OMVPE) on Ge substrates and analyzed by low-temperature photoluminescence (PL) spectroscopy. All spectra of thin GaAs on Ge show two different structures, one narrow band-to-band (B2B) structure at an energy of ~1.5 eV and a broad inner-bandgap (IB) structure at an energy of ~1.1 eV. Small strain in the thin GaAs films causes the B2B structure to be separated into a light-hole and a heavy-hole peak. At 2.5 K the good structural quality of the thin GaAs films on Ge can be observed from the narrow excitonic peaks. Peak widths of less than 1 meV are measured. GaAs films with thickness smaller than 200 nm show B2B PL spectra with characteristics of an n-type doping level of approximately 10 18 atoms/cm 3 . This is caused by heavy Ge diffusion from the substrate into the GaAs at the heterointerface between the two materials. The IB structure observed in all films consists of two gaussian peaks with energies of 1.04 eV and 1.17 eV. These deep trapping states arise from Ge-based complexes formed within the GaAs at the Ge-GaAs heterointerface, due to strong diffusion of Ge atoms into the GaAs. Because of similarities with Si-based complexes, the peak at 1.04 eV was identified to be due to a Ge Ga -Ge As complex, whereas the peak at 1.17 eV was attributed to the Ge Ga -V Ga complex. The intensity of the IB structure decreases strongly as the GaAs film thickness is increased. PL intensity of undoped GaAs films containing anti phase domains (APDs) is four orders of magnitude lower than for similar films without APDs. This reduction in intensity is due to the electrically active Ga-Ga and As-As bonds at the boundaries between the different APDs. When the Si-doping level is increased, the PL intensity of the APD-containing films is increased again as well. A film containing APDs with a Si doping level of ~10 18 atoms/cm 3 has only a factor 10 reduced intensity. We tentatively explain this observation by Si or Ge clustering at anti phase boundaries, which eliminates the effects of the Ga-Ga and As-As bonds. This assumption is confirmed by the fact that, at 77 K, the ratio between the intensity of the IB peak at 1.17 eV to the intensity of the peak at 1.04 eV is smaller than 1.4 for all films containing APDs, whereas it is larger than 1.4 for all films without APDs. This shows stronger clustering of Si or Ge in the material with APDs. For future electronic applications, Ge diffusion into the GaAs will have to be reduced. PL analysis will be a rapid tool for studying the Ge diffusion into the GaAs thin films.

Epitaxial growth of highly mismatched III-V materials on (001) silicon for electronics and optoelectronics

“…APBs are electrically charged planar defects, acting as non-radiative recombination centers in optoelectronic devices and leakage paths in electronic devices. The impact of APBs on the optical properties of III-V layers is often characterized by photoluminescence quenching and spectral broadening [28,29], while their role on electrical properties is relected in the significantly degraded electron mobilities [29,30]. With certain growth or etching conditions, APBs rising to the material surface could be visible under scanning electron microscopy (SEM) or atomic force microscopy (AFM).…”

Cathodoluminescence Study of Orientation-Patterned GaAs Crystals for Nonlinear Optics

“…On the other hand, the lateral extension of the shadow area around the domain walls is around 2 lm to 3 lm on each side, which is the result of the diffusion of the minority carriers towards the APBs; the antibonds As-As and Ga-Ga are active nonradiative recombination centers. 9 Nevertheless, the quenching of the CL at the domain walls is less intense than expected for the activity of the antibonds. On the other hand, the dark area surrounding the APBs revealed by CL is not uniform, suggesting an irregular domain wall recombinative atmosphere; this suggests that the domain walls are gathering defects which partially suppress the antibonds, with corresponding fluctuations in the nonradiative recombination activity along the domain walls.…”

High quality GaAs quantum nanostructures grown by droplet epitaxy on Ge and Ge‐on‐Si substrates

“…The presence of contamination due to Ge atoms in the GaAs and AlGaAs layers grown on Ge and Ge-on-Si substrates is not surprising and well described in scientific literature (e.g. [21,22]). The PL signal observed in sample B and C around 1.7 eV could be attributed to the presence of impurities and defects inside the AlGaAs barrier, as reported in [23].…”