Surface photovoltage spectroscopy of metamorphic high electron mobility transistor structures

InAlAs∕InGaAs metamorphic high electron mobility transistor (MHEMT) epitaxial structures have been characterized using surface photovoltage spectroscopy (SPS). The measurements have been extended to pseudomorphic high electron mobility transistor (PHEMT) epitaxial structures and to complete devices. The direct current characteristics of the latter were also measured. An empirical model, which correlates the top and bottom delta-doping concentrations (δtop and δbot) and the surface charge density Qsur with spectral features, has been applied to the MHEMT and PHEMT structures before and after processing. The results show correlations between extracted Qsur and the measured threshold voltage and drain saturation current of the devices. The analysis shows general correlations between epistructure parameters and final device performance and indicates the universality of the model for the different HEMT structures. Thus, SPS is sensitive not only to epitaxial structure parameters but to final device performance...