Surface processes in OMVPE - the frontiers

Gb. Stringfellow et al., Surface processes in OMVPE - the frontiers, J CRYST GR, 221, 2000, pp. 1-11
Citations number
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
ISSN journal
0022-0248 → ACNP
Year of publication
1 - 11
SICI code
Surface processes have long been known to be an important part of any epita xial growth process. These processes are closely linked to the surface stru cture. However, until recently, the surface structure and the surface proce sses were difficult to study experimentally for conventional vapor-phase ep itaxy (VPE) and liquid-phase epitaxy. Recently, optical techniques such as surface photo absorption (SPA) have been developed to the point that they g ive useful information about the surface reconstruction in situ during orga nometallic vapor-phase epitaxial(OMVPE) growth. Thus, they can in many case s be used to monitor the surface processes. A powerful method for controlli ng the surface structure during epitaxial growth using surfactants has rece ntly emerged. This work describes the use of the surfactants Te, a donor, a nd As, Sb, and Bi, elements that are isoelectronic with P, on the propertie s of GaInP grown by OMVPE. These surfactants are found to significantly aff ect the microscopic arrangement of Ga and In atoms in the bulk solid by eff ecting a change in the surface structure. CuPt ordering is ubiquitous in II I/V semiconductor alloys. It is significant because of the dependence of ba ndgap energy on the degree of order. The CuPt structure is formed due to th e strain induced by the formation of [(1) over bar 1 0] P dimers on the sur face. Each of the surfactants studied is found to result in disordering for layers grown using conditions that would otherwise produce highly ordered GaInP. Te yields disordered material with no change in the SPA spectra. How ever, the step velocity is found to increased markedly. Thus, the effect ap pears to be kinetic. Sb causes disordering due to a replacement of [(1) ove r bar 1 0] P dimers on the nominally (0 0 1) surface by larger Sb dimers, w hich reduces the strain-induced driving force for CuPt ordering at the surf ace. Thus, the effect is due to surface thermodynamics. For high Sb concent rations in the vapor, a triple-period ordered structure is formed. The appe arance of this phase coincides with a distinct change in the surface recons truction as indicated by SPA spectroscopy. Modulation of the TESb flow rate during growth was used to produce an abrupt order/disorder heterostructure with a bandgap energy difference of 135 meV with no significant change in solid composition at the interface. SPA results show that addition of As du ring growth also reduces the degree of order by displacing some of the [(1) over bar 1 0] P dimers on the surface. In this case, significant As concen trations in the solid of a few percent are observed. Thus, As is not an eff ective surfactant. Addition of Bi during growth results in a change in the surface reconstruction, as indicated by SPA spectroscopy, for Bi concentrat ions producing disordered GaInP. Unlike Sb and As, the Bi also causes a mar ked increase in the step velocity coincident with the loss of order. For si ngular (001) substrates, island formation is suppressed by Bi, resulting in the growth of much smoother layers. Modulation of the TMBi concentration d uring growth has been used to produce disorder/order heterostructures. The use of isoelectronic surfactants during growth to influence the properties of a semiconducting solid is a new and exciting development in control of t he OMVPE growth process. It is expected that the use of isoelectronic surfa ctants to determine the surface reconstruction will find application in the growth of complex device structures. It also appears likely that this will be useful for controlling other characteristics of the growth process and the properties of the resultant semiconductor materials. (C) 2000 Elsevier Science B.V. All rights reserved.