The change of resistance of

n

-type

Ga ({As}_{1 - x} P_{x})

samples under hydrostatic pressure up to 15 000 atm was measured between 190 and 363°K. Large pressure-dependent resistance changes were observed for samples with

x \approx 0.35

. These observations are consistent with the presence of another conduction band edge of much lower mobility presumably along

k = (100)

into which electrons are transferred when the relative energy separation between the two edges is lowered by pressure. The measured results are compared with calculations based on the model proposed by Ehrenreich. The agreement between theory and experiment is found to be good if certain parameters are varied in a systematic way. For lightly doped material the mobility ratio of electrons in the light mass band to those in the heavy mass band is found to be large and to decrease rapidly with increasing temperature. At higher carrier concentrations both the magnitude of the mobility ratio as well as its variation with temperature are substantially reduced. At 300°K the (000) and (100) minima are found to cross at

x \approx 0.44

if we assume Vegard's law to be valid. The experimental data are best explained if it is assumed that the separation between the two sets of minima changes at a rate of >1×

10^{- 4}

eV/°K.

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