Parasitic Interlayer at the GaAs-on-InGaP Interface in MOVPE InGaP∕GaAs: A Study by the Chemically Sensitive (200) Diffraction

Abstract

The chemically sensitive (200) diffraction in the dark field (DF) mode of transmission electron microscopy has been used to detect, identify, and evaluate the composition of the parasitic interlayer at the GaAs-on-InGaP interface in metallorganic vapor-phase epitaxy (MOVPE) normalInxnormalGa1−xP∕GaAs heterostructures. The latter were grown at 600°C with no growth interruption. The composition range determined by (200) DF was further refined by using the X-ray diffraction result that the interlayer has a negative lattice mismatch to GaAs. The parasitic interlayer can be either GanormalAs0.45normalP0.55 or normalInxnormalGa1−xnormalAs1−ynormalPy with 0⩽x<0.069 and 0.55⩽y<0.707 . P∕As intermixing and In segregation are assumed to drive the formation of the interlayer. The low In content in the quaternary is ascribed to the reduced In segregation at 600°C . In segregation is likely favored by the tensile strain associated with the interlayer in its process of growth.

CL and dark field TEM analysis of composition change at interfaces in InGaP/GaAs junctions grown by MOCVD

“…The stoichiometry of the sublayers 1 and 2 as determined by TEM indicates a slight In and P enrichment of the nominal GaAs QW that thus changes its nature. Such enrichment should be caused by P/As intermixing at the inverted interface and In segregation in the growth direction as discussed elsewhere [5,10,[15][16][17]. TEM further shows the fine structure of the modified nominal GaAs QW, i.e., the presence of two sublayers, one more In and P rich closer to the undergrown InGaP layer and a second one less In and P rich far from it.…”

“…They both suggest that at the inverted GaAs-on-InGaP interface there is the formation of an extra quaternary layer of InGaAsP inside and replacing the nominal GaAs QW layer as suggested in several works [5,10,[15][16][17]. The formation of just InGaAs as sublayer 1 might be less likely because it might easily happen that residual P atoms, remained in the reactor after the PH 3 flow had been switched off, are incorporated in the first monolayers of the GaAs QW since Ga prefers to bond to P rather than to As [18], as far as P atoms are available.…”

“…1 where the CL emission A of the sample studied here is compared with the peak B of the GaAs QW (1.56 eV @ 77K) observed in a structure of type a), GaAs substrate/AlGaAs/GaAs/InGaP [6,7]. [8][9][10]. The kinematical approximation is used as the images were acquired in thin areas of the TEM specimen.…”

“…An alloy looks darker than GaAs when C 200 is < 1. C 200 depends on the square of the composition as so does F 200 2 [8][9][10]. Figure 3 shows computed plots of C 200 for In x Ga 1-x As and GaAs 1-y P y .…”

Precise structure control of GaAs/InGaP hetero-interfaces using metal organic vapor phase epitaxy and its abruptness analyzed by STEM

“…However, fabrication of abrupt hetero-interfaces in InGaP/ GaAs systems by metal organic vapor phase epitaxy (MOVPE) is more difficult than that in AlGaAs/GaAs, mainly due to the exchange between As and P [13][14][15][16]. Other factors that contribute to the difficulty are the ordering effect of InGaP and the segregation of In in the InGaP layer.…”