Distribution of Impurities in Zn,O‐Doped GaP Liquid Phase Epitaxy Layers

Abstract

A series of variously doped liquid phase epitaxy (LPE) layers were analyzed to establish the distribution of Zn,O and residual impurities contributing to the net impurity gradient previously observed in the p‐layer of high efficiency LPE diodes. From these experiments we conclude that the net impurity gradient is primarily a consequence of a decreasing Zn concentration along the growth direction, and, to a lesser degree, an increasing residual donor concentration. The distribution of intentional and unintentional impurities was found to be independent of substrate doping level.The effect of cooling rate on the various impurity distributions was also studied, covering the range 0.5°–18°C/min. Residual impurity levels and associated gradients were significantly reduced by decreasing the cooling rate which indicates that residual impurity incorporation is kinetically controlled, probably by slow diffusion of these impurities in front of the growing LPE layer. Similarly, the O level appears to be decreased by reduced cooling rate. In contrast, Zn doping was found to be independent of cooling rate which suggests that its incorporation was essentially under equilibrium conditions. Assuming this to be the case, we have shown that the observed Zn distribution is consistent with the temperature dependence of the Zn solid solubility. Using an equilibrium description for Zn incorporation, we have computed the near‐junction Zn and O concentrations in the previously reported high efficiency diodes to be , respectively. The corresponding level of residual impurities yields a net donor concentration of .