GAS-SOURCE MOLECULAR-BEAM EPITAXY GROWTH OF INALP BAND-OFFSET REDUCTION LAYERS ON P-TYPE ZNSE

One of the major problems in the application of wide-band gap II-VI co mpound semiconductors to laser diodes is the difficulty of achieving l ow resistance ohmic contact to p-type ZnSe due to the large valence ba nd 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 b eam epitaxy). It is found that the surface morphology of the In0.5Al0. 5P layers grown on (001) ZnSe becomes better as growth temperature is decreased. In the initial stage of InAlP growth on ZnSe, the facets ar e formed and a rough surface morphology is produced at a high growth t emperature of 500 degrees C. Lower temperature growth at about 350 deg rees C and the use of the MEE (migration enhanced epitaxy) growth meth od produces a better surface morphology. Be doping of InAlP layers at low growth temperatures is also studied. It is found that hole concent rations as high as 2x10(18) cm(-3) are easily obtained for p-type InAl P layers grown at 350 degrees C, although a higher Be cell temperature is required than that for a 500 degrees C grown p-type InAlP. These r esults suggest that the Be-doped InAlP layer can be used as an interme diate layer to form the low resistance ohmic contact to p-type ZnSe.