Influence of the degree of order of InGaP on its hardness determined using nanoindentation

Spontaneous atomic ordering takes place during metal-organic vapor phase epitaxy when certain semiconductors alloys start forming long-range arrangements different from their standard lattice unit cells. In the case of InGaP, a zincblende semiconductor, the ordered CuPt(B) structure consists of alternating Ga and In rich ( 1 ¯ 11 ) and ( 1 1 ¯ 1 ) planes. In this investigation, InGaP was deposited on (001) Ge wafers with a 6° miscut toward the [111] direction in two consecutive experiments. A surfactant was used in experiment A while depositing InGaP to induce a lower degree of order. high resolution x-ray diffraction was used to calculate composition and strain of the InGaP epilayers. The symmetric (004) as well as the asymmetric (224) glancing exit reflections were used. The results enabled the extraction of a theoretical band gap energy E g corrected for strain effects. Photoluminescence was used to measure the actual E g . By comparing the two, the degree of order η was determined to be 0.12-0.15 for wafers from experiment A and 0.43-0.44 for wafers from experiment B. Atomic force microscopy AFM demonstrated that all experimental wafers had a surface rms roughness of 6.1-7.4 Å. Extensive nanoindentation measurements were performed on samples from both experiments. It was determined that the degree of order has no effect on the nanoindentation hardness of InGaP. Using 1/2 (115) superlattice reflection scans, the InGaP ordered domains size was estimated to be 28.5 nm for sample B1. No superlattice peak was detected in sample A1. The large ordered domain size in B1 explains why no order-hardening behavior was observed in InGaP.