Bias dependence and light sensitivity of (Al, Ga)As/GaAs MODFET's at 77 K

Modulation doped field-effect transistors typically show a threshold-voltage shift of about 0.2 V at 77 K with respect to room temperature. An investigation of the characteristics of Al0.33Ga0.67As/ GaAs and Al0.24Ga0.76As/GaAs MODFET's confirms that the low temperature performance of these devices is affected by the presence of persistent photoconductive traps in the bulk (Al, Ga) As and the properties of the surface, both of which depend strongly on the Al mole fraction and the growth conditions. Al0.33Ga0.67As/GaAs MODFET's grown at 610°C show a threshold voltage shift of less than 0.05 V at 77 K with respect to room temperature and little sensitivity of the current-voltage characteristics on illumination and on bias condition, indicating that by proper control of the growth parameters it is possible to obtain high quality (Al, Ga)As/GaAs MODFET's suitable for operation 77K.