Electrical properties of CdS-GaAs heterojunctions

Conclusions

CdS -GaAs heterojunctions have been shown to be sharp. The potential barrier is almost entirely located on the GaAs side and its height, equal to 0.7 eV, is determined by surface states. The current transport mechanism in CdS-GaAs heterojunctions depends on the density of free-charge carriers in the GaAs, temperature, and on the type of heterojunction. It has been shown that:

• a) For a forward voltage in heterojunctions with a low GaAs free-carrier density (n < 10¹⁷ cm⁻³ and p < 10¹⁸ cm⁻³) it is above-barrier emission of charge carriers that occurs at room temperatures. At lower temperatures the current in like-type heterojunctions is probably due to electron tunneling and the recombination component, and in unlike-type heterojunctions to multistep tunneling. In heterojunctions with a high carrier density in the GaAs (n > 10¹⁷ cm⁻³ and p > 10¹⁸ cm⁻³) thermostimulated cold emission dominates in like-type heterojunctions and multistep tunneling in unlike-type heterojunctions (in the temperature interval 77–400°K);

• b) For a reverse voltage the current in like-type heterojunctions is due to carrier generation in the GaAs space-charge layer and probably to generation from surface states, and in unlike-type heterojunctions to the tunnel passage of electrons from the valence band of GaAs to the conduction band of CdS.