Gas source molecular beam epitaxy growth of InAlP band offset reduction layers on p-type ZnSe

Abstract

One of the major problems in the application of wide-band gap II–VI compound semiconductors to laser diodes is the difficulty of achieving low resistance ohmic contact to p-type ZnSe due to the large valence band offset between metal electrode and ZnSe. To solve this problem, the use of an intermediate p-type InAlP layer to p-type ZnSe as a valence band offset reduction layer is studied by gas source MBE (molecular beam epitaxy). It is found that the surface morphology of the In 0.5Al 0.5P layers grown on (001) ZnSe becomes better as growth temperature is decreased. In the initial stage of InAlP growth on ZnSe, the facets are formed and a rough surface morphology is produced at a high growth temperature of 500°C. Lower temperature growth at about 350°C and the use of the MEE (migration enhanced epitaxy) growth method produces a better surface morphology. Be doping of InAlP layers at low growth temperatures is also studied. It is found that hole concentrations as high as 2 × 10 18 cm −3 are easily obtained for p-type InAlP layers grown at 350°C, although a higher Be cell temperature is required than that for a 500°C grown p-type InAlP. These results suggest that the Be-doped InAlP layer can be used as an intermediate layer to form the low resistance ohmic contact to p-type ZnSe.