Growth rate dependence on GeH4 during gas source MBE of SixGe 1-x alloys grown from Si2H6 and GeH4

Abstract

The epitaxial growth of Si and SixGe1-x alloys from molecular beams of gaseous Si (Si2H6) and Ge (GeH4) hydrides on Si(001) substrates (Si-GSMBE) has been studied using reflection high energy electron diffraction (RHEED). Diffraction patterns reveal that Ge deposited on Si results in a Stranski-Krastanow growth mode with a change in surface reconstruction in the two-dimensional (2D) regime from the two-domain Si(001)-(2×1) to a two-domain Si(2×8)-Ge, prior to the onset of three-dimensional (3D) growth. Using the RHEED intensity oscillation technique during alloy growth it is found that at substrate temperatures below 600°C there is an enhancement in growth rate of the alloy above that of pure Si growth from disilane. This phenomenon has been attributed to the increased desorption rate of hydrogen adatoms due to the presence of Ge, which leads to an acceleration of the heterogenous reaction rate. Consistent with this, during growth at substrate temperatures above the desorption rate maximum for hydrogen, 600°C no enhancement of the growth rate due to the addition of GeH4 to the beam flux is observed and the growth rate is dependent upon disilane arrival rate. Reaction kinetics are discussed in terms of Ge concentration in the films and the ratio of GeH4 to Si2H6 in the incident beams under various growth conditions. © 1993.