Effect of indium mole fraction on charge control, DC and RF performance of single quantum-well InP/InxGa1-xAs/InP (0.53⩽x⩽0.81) HEMTs

During the past several years, HEMT structures on InP have attracted much attention in high-speed digital and millimeter wave device applications. Devices which use In_xGa_1-xAs channel on InP substrates (x⩾0.53) show better performance than those on GaAs (0⩽x0.3) because of the enhanced low-field mobility, peak- and saturation velocities as well as carrier concentration in the case of indium-rich channels. Therefore, the most effective way to improve both DC- and RF-characteristics of these devices is to increase x as high as possible without device degradation by channel relaxation. A very promising alternative to conventional InAlAs/InGaAs/InP HEMTs are the InP/In_xGa_1-xAs/InP pseudomorphic HFETs. In these devices the instable Al-containing material InAlAs is replaced by InP for both barrier and carrier supplying layers. In order to improve the Schottky characteristics on InP a thin, highly doped and depleted p-InP barrier enhancement layer is utilized. In the recent past very good results have been achieved using this approach. In this study we present a systematical investigation about the influence of excess indium in the channel of five LP-MOVPE grown single quantum-well (SQW) InP/In_xGa_1-xAs/InP (x=0.53, 0.6, 0.67, 0.74 and 0.81) HEMTs