Droplet-induced dot, dot-in-hole, and hole structures in GaGe thin films grown by MOCVD on GaAs substrates

Abstract

We report observations and origins of Ga-rich GaGe droplets and the localized etching of Ge-rich GaGe thin films grown on GaAs (100) substrates by metalorganic chemical vapor deposition. Micron and sub-micron dots, dot-in-holes, and holes have been fabricated by controlling the partial pressures of the Ga and Ge precursors as well as the substrate temperatures. The dot-in-hole features can also be converted to empty holes via post-growth sonication in hot deionized water due to the low melting point of the Ga-rich dots. Enhanced Raman scattering (ERS) of the Ge-Ge lattice vibrational mode has been observed at the wall of the concentric dot-in-hole structures as well as in the empty holes. To interpret the ERS mechanism, we have carried out finite-difference time-domain (FDTD) simulations, which reveal an enhanced electrical field for the obtained structures as a result of interference between the incident and reflected waves at the surface of the thin films that, in turn, results in the observed ERS. These findings greatly enrich the conventional droplet epitaxy and etching techniques and widen their applications.

High-resolution X-ray diffraction and micro-Raman scattering studies of Ge(:Ga) thin films grown on GaAs (001) substrates by MOCVD

“…More detailed growth parameters and procedures can be found in our earlier publications. 11,12 For the current study, three kinds of samples were selected. Sample A was unintentionally doped, $10 mm in thickness, and grown at 575 C; sample B was Ga-doped, $1.0 mm thick, grown at 550 C; and sample C was heavier Ga-doped than sample B, $1.0 mm thick, grown at 600 C. They are summarized in Table 1.…”

“…However, their relative variations as a function of the growth temperatures are consistent with the evolution of the surface dot structures (see ref. 12) and thus can be a relative indicator of Ga incorporations. present RSMs, carried out in an asymmetric conguration with a high incident angle aiming at the Ge(:Ga) (115) and GaAs (115) atomic planes, of samples A and C, respectively.…”

“…1(c)-(d) of sample C and detailed dot-formation mechanism in ref. 12]. Localized EDX analysis on the lm surface, at the at areas away from the dot structures, reveals that the Ga concentration increases from 5.2% to 5.6% and 5.8% when the growth temperature is increased from 550 C (sample B) to 600 C (sample C) and 630 C, respectively.…”

“…Here, q GaAs is the Bragg angle of GaAs (004) and Dq is the angle difference between the diffraction peaks of GaAs (004) and Ge(:Ga) (004). Together with the inplane lattice constants obtained above, the lattice constant of fully relaxed Ge(:Ga), a Ge(:Ga) , can be obtained via 3 t ¼ (À2C 12 …”

Enhanced photoemission from surface modulated GaAs:Ge

“…Surface modulation on nanoscale may be brought up on a Ge surface by annealing a thin Ge-layer on GaAs substrate. The mechanism behind the formation has been explained on the basis of phase separation and surface segregation of Ga due to low solubility of Ga in Ge, [30] and Ge diffusion into GaAs via Ga vacancies. [27,31,32] Notably, use of high temperature processing of such structure is restricted since Ge forms a eutectic alloy with GaAs at 865 • C. [7,29] Our present paper describes the fabrication and characterization of a GaAs:Ge based photocathode (emitter) with effective PE characteristics under illumination by a simple and low-cost commercially available UV (∼265 nm) LED, having low optical power, but sufficient energy to excite the photoelectron from GaAs into vacuum level.…”