• PDF / 1,968,921 Bytes
• 6 Pages / 414.72 x 648 pts Page_size
• 53 Downloads / 252 Views

DOWNLOAD

REPORT

---

A common problem in GaP/Si is three-dimensional (3-D) nucleation of GaP layers in the initial stages of heteroepitaxy [8-10]. Another common defect in III-V/Si heteroepitaxy is the formation of anti-phase domains (APDs) and anti-phase domain boundaries (APBs) upon their coalescence. As in the case of GaAs/Si, the APB problem seems to be insignificant when Si(100) off-cut, Si(1 11) or Si(21 1) substrate orientations are used [6,11]. However, there is no conclusive evidence to support this observation in GaP/Si heteroepitaxy. In this study, GaP/Si films were grown using atmospheric pressure MOCVD and MBE under a variety of processing conditions and substrate orientations. The films were characterized using transmission electron microscopy (TEM) primarily, to study the defect structure commonly observed in these materials and understand the origin of these defects. EXPERIMENTAL The GaP/Si films processed using MOCVD were grown using the popular two-step technique in III-V/Si heteroepitaxy. The two-step technique involved the growth of a thin GaP "buffer" layer at a low temperature and subsequent GaP growth at a high temperature to the required thickness. The Si substrate orientations chosen for MOCVD growth of GaP/Si were Si(1 11) and Si(100) 6" off-cut towards [110]. These orientations were chosen primarily to avoid the APB problem, commonly encountered in III-V growths on Si(100) substrates. The GaP layers were grown using trimethylgallium (TMG) and phophine (PH 3 , 10% H 2 ) as reactants in an atmospheric pressure MOCVD reactor. Prior to growth, the Si substrates were annealed at =1050" C for 30 minutes to desorb the oxide and any other contaminants that might not have been 431

1996 Materials Research Society Mat. Res. Soc. Symp. Proc. Vol. 399 ©

(b)

(a)

Fig.l.(a)An SEM micrographof the surface of MBE grown GaPISi(100) 4 off-cut substrate;An SEM micrographof the surface of MOCVD grown (b) GaPISi(111), (c) GaPISi(100)6 *off-cut.

(c) removed by the ex-situ substrate cleaning procedure. The buffer GaP layer (=0.04jgm) was typically grown at 400' C. During some of the growth runs, a post-buffer anneal at 800' C was employed to obtain a better homoepitaxial GaP surface prior to the growth of the final GaP layer (-0.96gm) at 700" C. The MBE processed samples were grown on Si(100) exact, Si(100) 4" off-cut towards [110] and Si(100) 8' off-cut towards [110]. The Si substrate wafers were cleaned thoroughly by soaking in a strong 'Piranha' solution (H2SO4 + H202) for 20 minutes, followed by a buffered HF dip and deionized water rinse. The process was repeated three times before loading the wafer for epitaxy. An in-situ anneal at -1000" C was carried out to desorb any native oxide remaining on the Si substrate prior to deposition of GaP layer. The GaP films ("'0. Igm) were grown in a single step at 640" C using elemental gallium (Ga) and red phosphorus (P4 cracked into P2 prior

432

to deposition) sources. Most of the GaP films processed using MBE were Ga terminated; that is, Ga was the first monolayer grown on the Si