Suppression of Rotational Twin Formation in Virtual GaP/Si(111) Substrates for III–V Nanowire Growth

Abstract

Planar GaP epilayers on Si(111) are considered as virtual substrates for III–V-related optoelectronic devices such as high-efficiency nanowire-based tandem absorber structures for solar energy conversion, next generation LEDs, and fast photodetectors. Rotational twin domains in such heteroepitaxial epilayers are found to strongly impede vertical nanowire growth. We investigate the twin-induced defect density and surface morphology of B-type GaP/Si(111) virtual substrates in dependence on the GaP nucleation process by metalorganic chemical vapor deposition. By employing quantitative high-resolution X-ray diffraction (HR-XRD)), scanning electron and atomic force microscopy (SEM and AFM), we reveal the significant influence of nucleation temperature and substrate miscut direction on the formation of rotational twin domains during a two-step GaP growth approach. The epilayer defect density is drastically decreased by low temperature GaP nucleation on Si(111) misoriented 3° toward [1̅1̅2], where rotational twin domains are suppressed below 5% and the layers exhibit a smooth surface morphology. We demonstrate that these virtual substrates are highly suitable for vertical GaP nanowire growth.

Effect of germanium auto-diffusion on the bond lengths of Ga and P atoms in GaP/Ge(111) investigated by using X-ray absorption spectroscopy

“…1(e) and 1(f) show ' scans of S 1 and S 2 ]. From the relative intensity of the ' scans the extent of the micro-twin-ning is estimated to be 32.24% and 39.43% for S 1 and S 2 , respectively (Roychowdhury et al, 2017;Koppka et al, 2016). A detailed discussion on the ' scans of these samples has been reported earlier (Dixit et al, 2014).…”

“…The residual strain may also occur due to the presence of micro-twinning and allotropes (wurtzite and zinc-blend phase) formation which has been observed from ' scans of HRXRD and Raman experiments (Aggarwal et al, 2018;Dixit et al, 2014). However, it has been reported that the micro-twinning fraction is largely reduced in the twostep growth process and becomes annihilated near the interface (Koppka et al, 2016). Thus, the effect of this microtwinning would be more prominent in S 1 (nucleating layer) compared with S 2 .…”

“…Sample S 1 (nucleating layer) is island-type GaP with partial coverage of the Ge substrate (Roychowdhury et al, 2017;Dixit et al, 2014). Sample S 2 contains a nucleating layer of 60 nm at low temperature, 425 C, followed by a thick layer, $ 760 nm, at a high temperature of 770 C. This growth process is referred to as the two-step growth process and detailed growth conditions are reported elsewhere (Dixit et al, 2008(Dixit et al, , 2014Navarro et al, 2017;Koppka et al, 2016;Volz et al, 2011). Sample S 1 was grown for investigating the morphology, crystalline quality and other optical properties of the nucleation layer of GaP which precedes the growth of the thick layer.…”

“…However, the most difficult part of such integration remains unsolved, i.e. preventing the occurrence of anti-phase domains, stacking faults and auto-diffusion of group IV elements in the grown structures (Morizane, 1977;Guo et al, 2012;Dixit et al, 2014;Koppka et al, 2016;Galiana et al, 2008;Bracht et al, 2009;Aggarwal et al, 2019;Roychowdhury et al, 2019). In order to overcome the generation of stacking faults in the nanostructure of these materials, the tensile strain based (111) surface is preferred because it does not allow the glide of 90 partial dislocations and limits the nucleation kinetics of 60 dislocations (Kvam & Hull, 1993;Maré e et al, 1987).…”

Mechanism of twin-reduced III-V epitaxy on As-modified vicinal Si(111)

“…1 and Ref. [25]), which we denote as α and β, respectively. Especially for polar compound semiconductors, it can be assumed that incoherent (often referred to as lateral ) twin boundaries have net charges [26] and hence a non-negligible impact on the optoelectronic properties [27,28].…”