Drift region characteristics of InP-based HEMT devices evaluated by a simple drift region model

InP-based HEMTs exhibit superior high frequency performance compared to GaAs PS-HEMTs. This is commonly attributed to a higher electron mobility, saturated velocity and better carrier confinement in the GaInAs QW-channel. Whereas the parameters determining f_t are well documented, the influence of the carrier confinement and electron dynamics on f_max is less clear. Intrinsically, a high f_max relies essentially on the efficiency of the gate-drain high field drift region to separate input and output. Thus, the impact of this region on f_max has been extensively studied analytically and numerically in the past. Due to the complex electron dynamics involved and the 2D-nature of this region, most models are limited to specific structures and only few general design criteria exist. In this study three structures are compared: an AlInAs/GaInAs HEMT structure on InP is analysed in detail and compared with a GaAs PM-HEMT device and a novel InP-based HEMT structure containing a composite GaInAs-InP QW channel. As mentioned above, the high f_max of InP-based HEMTs is generally attributed to an improved hot electron confinement. The analysis presented here, however, reveals that the high f_max of the InP-based devices is mainly linked to an extended lateral drift region and not to an improved carrier confinement