Doping level anomalies resulting from exposure to dopant precursors during cooling in MOVPE

Abstract Exposure of InP doped with Zn, Cd, Mg or Be to DMZn during cooling from typical MOVPE growth temperatures results in a drop in doping level at the surface of more than an order of magnitude, the doping level rising with distance from the surface. The result is very similar to that obtained on cooling in AsH 3 , which has previously been shown to be the result of passivation by H coming from the AsH 3 pyrolysis. However, little or no H is found in such samples, even when PH 3 is present during cooling. SIMS shows that, on cooling, large quantities of dopant diffuse in from the ambient. We suggest that this excess dopant lies in interstitial sites and compensates the existing substitutional atoms, reducing the p-doping level. The low concentration of H found in these crystals is attributed to occupation of their preferred sites by interstitials.