Enhancement of electron transport mobility in GaAs/InGaAs asymmetrically doped narrow quantum well pHEMT structure

We study the effect of asymmetric doping concentrations on the electron mobility mu in GaAs/InGaAs-based single quantum well (SQW) as well as double quantum well (DQW) pseudomorphic high electron mobility transistor (pHEMT) structures. Unequal doping in the substrate and surface barriers (n(d1) and n(d2)) causes asymmetric distributions of subband wave functions, psi(0) and psi(1,) which influence the subband scattering rate matrix elements (SSRME), thereby affecting the subband mobility mu(n). For narrow well widths (w(w)), in SQW structures, mostly a single subband is occupied. We show that an increase in n(d2), keeping n(d1) fixed, enhances mu nonlinearly. The interface roughness (ir-) scattering mostly dominates mu in thin wells (w(w) < 70 & Aring;), while generally, mu is determined by ionized impurity (ii-) scattering and to some extent by alloy disorder (ad-) scattering. The influence of ir-scattering enhances, while ad-scattering diminishes, by reducing n(d2). For DQW, a double subband is occupied. In a symmetric DQW structure at resonance, n(d1) = n(d2), psi(0) and psi(1) equally extend into both the wells. For a minor variation, say n(d1) > n(d2), psi(0) mostly lies in one well while psi(1) is in the other well. In the case of n(d1) < n(d2), the distribution reverts. The substantial changes in psi(0) and psi(1) influence the intra- and inter-SSRME differently through intersubband effects, leading to nonlinear mu(n) as a function of n(d2). Taking n(d1) + n(d2) = 3 x 10(18) cm(-3), we show that for w(w1) = w(w2) = 80 & Aring;, a shallow dip in mu occurs at n(d1) = n(d2) = 1.5 x 10(18) cm(-3). Whereas, for w(w1) = 60 & Aring; and w(w2) = 100 & Aring;, the dip in mu occurs near the corresponding resonance, n(d1) = 2.3 x 10(18) cm(-3) and n(d2) = 0.7 x 10(18) cm(-3). Our results of nonlinear mu can be utilized for performance analysis of pHEMT.

Automated summary

This study investigates the effect of asymmetric doping concentrations on the electron mobility in GaAs/InGaAs-based single and double quantum well pseudomorphic high electron mobility transistor structures. The results show that different doping concentrations lead to asymmetric distributions of subband wave functions, which in turn influence the subband mobility. It is found that increasing the doping concentration of one layer in a single quantum well structure enhances the mobility nonlinearly. In double quantum well structures, the distribution of subband wave functions changes depending on the relative doping concentrations, resulting in a nonlinear variation of the mobility.