Evaluation of III–V multilayer transport parameters using quantitative mobility spectrum analysis

Abstract

In this paper we illustrate the power and utility of quantitative mobility spectrum analysis (QMSA) of magnetic field dependent Hall data in order to evaluate the transport parameters of multilayer III–V materials and device structures such as high electron mobility transistors (HEMTs) and heterojunction bipolar transistors (HBTs). As a first example, we present the QMSA of a n +GaAs/GaAs/n +AlGaAs/p +GaAs/n GaAs/n +GaAs HBT structure, in which QMSA resolves two carrier species: holes with mobility of 700 cm 2 V −1 s −1 and density 1.6 × 10 18 cm −3, and electrons with mobility of 1530 cm 2 V −1 s −1 and density 3.0 × 10 18 cm −3. A direct comparison with the results of C-V electrochemical profiling indicates that all n +-type layers (sub-collector, emitter and cap) are characterised by an electron mobility which appears in the mobility spectrum as a single peak with an average density corresponding to the sum of all three n + layers. The peak in the hole spectrum may be clearly identified with the single p-type base layer. The second example is an n −1GaAs/n +AlGaAs/AlGaAs/GaAs HEMT structure in which the 2D electron gas population with a mobility of 7750 cm 2 V −1 s −1 and sheet density of 2.6 × 10 11 cm −2 is readily identified and separated from the mobility spectrum peak corresponding to the two highly-doped n-type capping layers. Due to the similar carrier mobility in both capping layers, their contribution to the spectrum appears as a single electron peak at 1100 cm 2 V −1 s −1 with a density of 2.1 × 10 16 cm −3.