Modulation Doped GaAs–Ga1-xAlxAs Heterostructures Grown by Atmospheric Pressure MOVPE

Abstract

Single and multiple period modulation doped GaAs–Ga_1-x Al _x As heterostructures have been grown by atmospheric pressure metalorganic vapour phase epitaxy (AP-MOVPE). Single period structures exhibit electron mobilities of 6700, 80000 and 90000 cm²·V^-1·s^-1 at 300 K, 77 K, and 4 K for a sheet carrier concentration of 7.4×10¹¹ cm^-2, 8.3×10¹¹ cm^-2 and 3.9×10¹¹ cm^-2 respectively. To our knowledge, these values represent the best mobilities reported in this structure grown by AP-MOVPE. Preliminary results on field effect transistors show a three fold increase of transconductance as temperature decreases from ambient to 77 K. Furthermore, we report mobility enhancement in “inverted” structures in which the conducting accumulation layers are located at the interfaces formed by growth of GaAs on top of (Ga, Alcp)As.