Minoritary Transport in Heavily Doped p-type and InGaAs
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Minoritary Transport in Heavily Doped p-type and InGaAs Eric Tea1 and Frederic Aniel1 1 Institut d’Electronique Fondamentale, UMR 8622 CNRS, Université Paris Sud 91405 Orsay Cedex, France. ABSTRACT Minoritary carrier’s transport properties are of fundamental importance for the HBT’s physics. The base transit time is a key parameter to improve microwave figure of merit. Some recent minoritary electron mobilities measurements versus acceptor doping level measured using magneto transport method exhibit a dramatic increase at very high majority carrier concentration. This effect has been attributed to the coupling of polar optical phonons with hole plasmons (LOPC) which controls the balance between enegy gain by electric field acceleration and energy loss by polar optical phonon emission. We present minoritary mobilities as a function of majority carrier doping calculated in the frame of electrons and holes Monte Carlo modelling including LOPC. INTRODUCTION The III-V ternary semiconductor InGaAs is an intensively used material for fast electronic devices because it can be lattice matched on InP (In0.53Ga0.47As) and have a high electron mobility. The properties of HBT transistors are controlled by minority carriers in heavily doped regions. Thus the knowledge of the minority carriers’ physical properties, such as their mobility, is required for designing devices. As the doping increases, it is expected that the minority carriers’ mobility decrease monotonously due to impurity (doping atoms) scattering and carrier-carrier collision which is not what happens. The measurement of minority electrons mobility in heavely doped p-type GaAs shows an increase for doping levels greater than 1019 cm-3 [1]. This mobility enhancement has been also measured in heavely doped p-type In0.53Ga0.47As [2]. This effect has been attributed to the coupling of polar optical phonons (POP) with hole plasmons (LOPC) [3] which changes the interplay between dominant elastic and inelastic scattering mechanisms. In the present paper, we present minority electrons’ mobility in heavily p-type doped In0.53Ga0.47As calculted via Monte Carlo modelling including LOPC. First, we summarize the content of the MC model and explain how we consider the phonon-plasmon coupling. Then, we show the calculated coupled modes scattering rates and mobilities. In the conclusion, we discuss the possible ways of improving the model. THEORY We use a Monte Carlo (MC) technique to solve the Boltzmann Transport Equation to calculate the charge carriers’ transport properties [4]. The model basically requires two sets of
parameters: one to describe the carriers’ interactions strength, and another one to describe the energy-wave vector relation (band structure). The first set of parameters, e.g. deformation potentials, are slightly fitted on measured low field drift mobilities (undoped) and velocity field characteristics. The second is taken as follows. The conduction band’s Γ valley is described by an isotropic and non parabolic valley. In the first conduction band
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