Abstract
Abstract
We study the effect of asymmetric doping concentrations on the electron mobility μ 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, ψ
0
and ψ
1, which influence the subband scattering rate matrix elements (SSRME), thereby affecting the subband mobility μ
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 μ nonlinearly. The interface roughness (ir-) scattering mostly dominates μ in thin wells (w
w
< 70 Å), while generally, μ 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
, ψ
0
and ψ
1
equally extend into both the wells. For a minor variation, say n
d1
> n
d2
, ψ
0
mostly lies in one well while ψ
1
is in the other well. In the case of n
d1
< n
d2
, the distribution reverts. The substantial changes in ψ
0
and ψ
1
influence the intra- and inter-SSRME differently through intersubband effects, leading to nonlinear μ
n
as a function of n
d2
. Taking n
d1
+ n
d2
= 3 × 1018 cm−3, we show that for w
w1
= w
w2
= 80 Å, a shallow dip in μ occurs at n
d1
= n
d2
= 1.5 × 1018 cm−3. Whereas, for w
w1
= 60 Å and w
w2
= 100 Å, the dip in μ occurs near the corresponding resonance, n
d1
= 2.3 × 1018 cm−3 and n
d2
= 0.7 × 1018 cm−3. Our results of nonlinear μ can be utilized for performance analysis of pHEMT.
Subject
Condensed Matter Physics,Mathematical Physics,Atomic and Molecular Physics, and Optics
Reference39 articles.
1. Pseudomorphic HEMT Technology and Applications;Ross,1996
2. Comparative study on nano-scale III-V double-gate MOSFETs with various channel materials;Nishida;Phys. Status Solidi,2013
3. Comparative assessment of III–V heterostructure and silicon underlap double gate MOSFETs;Pardeshi;Semiconductors,2012
4. Design of double deltadoped Al0.22Ga0.78As/In0.22Ga0.78As pseudomorphicHEMTs;Wang;Appl. Mech. Mater.,2012
5. Deeply scaled strained InGaAs HEMTs with improved injection velocity, IEDM;Kim;Tech. Digest,2009