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

Abstract

A series of variously doped normalGaP 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 normalGaP 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 6.7×1017 cm−3 normaland 2.7×1017 cm−3 , respectively. The corresponding level of residual impurities yields a net donor concentration of ≲3×1016 cm−3 .

The Solid Solubility Isotherms of Zn in GaP and GaAs

“…Values of xlzn for each melt were calculated by assuming the incorporation without loss of the total amount of Zn present in the Zn(POz)2. Figure 7 also illustrates the theoretical solubility isotherm for GaP at 1465~ in the immediate vicinity of Additional evidence to confirm the essential correctness of the low temperature isotherms is provided by the recent data of Saul and Hackett (29) on Zn incorporation in GaP, grown by liquid-phase epitaxy from an initial growth temperature of 1025~ and from a solution containing Xlzn = 3 x 10 -4. It has been shown by these authors that the Zn solubility in GaP, obtained by surface capacitance measurements and Zn ~5 tracer analysis, decreases from the growth interface (1025~ to the surface (~--770~ Furthermore, Saul and Hackett (29) have demonstrated by means of a detailed analysis that their experimental Zn distribution data (CSzn vs. distance from interface) compare favorably with the theoretical Zn profile calculated on the basis of the isotherms in Fig.…”

Progress in doping semiconductor nanowires during growth

“…As the doping precursor is switched off, the finite doping concentration in the droplet will gradually reduce to negligible values, which can only be accomplished through the gradual deposition of the 'stored' dopants in NW segments that are not intended to be doped. This effect is present in systems that crystalize from liquids, has been known for decades in liquid phase epitaxy, 60 and was recently discussed in the context of axial heterostructure NW growth. 61,62,63 In their LEAP studies, Connell et al also identified such doping gradients in a Ge NW as shown in Figure 7.…”

On the Incorporation of Oxygen in GaP Liquid Phase Epitaxy Layers

“…The addition of Ga203 results in compensation of Zn acceptors equivalent to an increase in donor concentration of 2.7 • 1017 atoms/cm 3, which has been interpreted to be entirely due to the deep O donor (9). To substantiate this interpretation, an O-doped LPE layer was grown using the same Ga~O3 addition.…”

“…Both Zn-and Zn,O-doped layers were grown on Tedoped (ND--NA~8 • 1017 ) SG or LEC (liquid encapsulation Czochralski) substrates using a fused quartz sealed-tube LPE system which has been described elsewhere (9). Except where indicated, layers were grown in evacuated ampoules which were cooled from 1025 ~ to 600~ at a rate of 10~…”