Characterization of multiple carriers in GaN using variable magnetic-field hall measurements

Variable magnetic-field Hall-effect measurements were performed on two thick GaN samples grown by hydride vapor-phase epitaxy (HVPE), one freestanding and one attached to the sapphire substrate. Results are compared to those obtained using the more standard, single magnetic-field Hall measurements. In both samples, a second low-mobility electron was indicated that significantly influenced interpretation of single-field Hall measurements, particularly at low temperatures. Extraction of the bulk carrier using fits to the variable-field Hall data allowed a more accurate determination of the temperature dependence of the bulk electrical properties and, hence, basic physical parameters. In addition, the quantitative mobility-spectrum analysis (QMSA) technique, reported here for the first time on GaN, indicated a continuous and significant spread in mobility for the bulk electron, likely with sample thickness. Thus, even the “improved” results, based on modeling the multiple-carrier fitting (MCF) analysis, obtained in this study should be viewed with some suspicion, as they clearly represent an average over an electrically inhomogeneous sample.     

Quantitative mobility spectrum analysis (QMSA) for hall characterization of electrons and holes in anisotropic bands

An extension of the quantitative mobility spectrum analysis (QMSA) procedure, which determines free electron and hole densities and mobilities from magnetic-field-dependent Hall and resistivity measurements, to materials exhibiting anisotropic conduction is presented. As test cases, the fully computer-automated procedure is used to analyze magnetotransport data from Bi thin films and Bi/CdTe superlattices. Using the results of the QMSA procedure, the thermoelectric properties of these films can be accurately modeled. As a second exmaple, an electron mobility anisotropy ratio of ≈4.5 is derived from the QMSA treatment of the Hall data for bulk Si samples.