OPTIMUM CHANNEL THICKNESS OF AL0.3GA0.7AS IN0.25GA0.75AS/GAAS HETEROSTRUCTURES FOR ELECTRON-TRANSPORT APPLICATIONS/

We have grown high-electron mobility transistor structures in the Al0. 3Ga0.7As/In0.25Ga0.75As/GaAs material system with In0.25Ga0.75As chann el thicknesses in the range 40-200 Angstrom. We have monitored the ons et of channel relaxation using Hall mobility measurements, polychromat ic cathodoluminescence mapping, time-resolved photoluminescence, trans mission electron microscopy, low-frequency noise,and deep-level transi ent spectroscopy measurements. It appears that the first relaxation sy mptom, the Stransky-Krastanow growth mode, is observed only by the las t three techniques. This shows that the onset of relaxation is not det ected by characterization techniques which measure global properties o f the material. On the other hand, it is detected by low-frequency noi se, deep-level transient spectroscopy, and transmission electron micro scopy measurements, which yield an estimation of the defect density in the material. (C) 1996 American Institute of Physics.