Positron annihilation in gallium phosphide

Long-slit angular distributions of positron annihilation radiation for the (100) and (111) directions of GaP are reported. The momentum distributions from the long-slit measurements are compared with recent Compton profile data to test the importance of the positron wavefunction and positron-electron correlations. Humps observed in the high-momentum region could be a band-structure effect and need not be of Umklapp origin. Autocorrelation function anisotropy suggests that the positron wavefunction is more correlated along the (111) bonding direction and the effect is stronger than that in elemental semiconductors.