Temperature Dependence of Charge Distributions and Carrier Mobility in an Undoped Si/SiGe Heterostructure

Capacitance–voltage (
${C}$
–
${V}$
) characteristics and carrier transport properties of 2-D electron gases (2DEGs) in an undoped Si/SiGe heterostructure at
${T}= {4} - {35}$
K are presented. Two capacitance plateaus due to density saturation of the 2DEG in the buried Si quantum well (QW) are observed and explained by a model of surface tunneling. The peak mobility at 4 K is 4.1
$\times 10^{{5}}$
cm
²
/
$\text{V}\cdot \text{s}$
and enhanced by a factor of 1.97 at an even lower carrier density compared to the saturated carrier density, which is attributed to the effect of remote carrier screening. At
${T}\,\,=35$
K, the mobility enhancement with a factor of 1.35 is still observed, which suggests the surface tunneling is still dominant.