EVALUATION OF III-V MULTILAYER TRANSPORT PARAMETERS USING QUANTITATIVE MOBILITY SPECTRUM ANALYSIS

In this paper we illustrate the power and utility of quantitative mobi lity spectrum analysis (QMSA) of magnetic field dependent Hall data in order to evaluate the transport parameters of multilayer III-V materi als and device structures such as high electron mobility transistors ( HEMTs) and heterojunction bipolar transistors (HBTs). As a first examp le, 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: h oles with mobility of 700 cm(2) V-1 s(-1) and density 1.6 x 10(18) cm( -3), and electrons with mobility of 1530 cm(2) V-1 s(-1) and density 3 .0 x 10(18) cm(-3). A direct comparison with the results of C-V electr ochemical profiling indicates that all n(+)-type layers (sub-collector , emitter and cap) are characterised by an electron mobility which app ears 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 ho le spectrum may be clearly identified with the single p-type base laye r. The second example is an ni GaAs/n(+)AlGaAs/AlGaAs/GaAs HEMT struct ure in which the 2D electron gas population with a mobility of 7750 cm (2) V-1 s(-1) and sheet density of 2.6 x 10(11) cm(-2) is readily iden tified 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 a ppears as a single electron peak at 1100 cm(2) V-1 s(-1) with a densit y of 2.1 x 10(16) cm(-3). (C) 1997 Elsevier Science S.A.