Mobility modulation of two-dimensional hole gas in a p-type Si/SiGe modulation doped heterostructure by back-gating

Abstract

The mobility limiting mechanism of a two-dimensional hole gas in a strained Si 0.8 Ge 0.2 /Si modulation doped heterostructure was investigated at 4.2 K by means of a back-gating measurement of the mobility. It was shown that the mobility decreased with increasing positive back-gate voltage at a fixed hole density. A self-consistent calculation of the wavefunction indicated that the wavefunction was pushed toward the hetero-interface when a more positive back-gate bias was applied. A comparison between the observed and the calculated mobility modulation due to the wavefunction deformation revealed that the Coulomb scattering by the ionized impurities in the spacer and/or at the hetero-interface limits the mobility.

Top-gating of p-Si/SiGe/Si inverted modulation-doped structures

“…Here, due to abnormal expansion and movement of the hole wave function with increasing hole density, there is a concomitant effect in decreasing of the efficiency of interface charge, roughness, and alloy scattering mechanisms. Despite this fact, the variations of Hall mobility with hole density ͑having downward curvatures͒ are rather similar to those in normal interface 4,8 and this is not understandable. Regarding that, we did not observe any pronounced difference in the mobility of holes confined at normal and inverted interfaces of Si/Si 0.8 Ge 0.2 /Si structures, 5 a theoretical calculation is needed to elaborate the role of these short range scattering mechanisms in limiting the mobility of holes at Si/SiGe/Si interfaces and explain these experimental results.…”

“…5,6 Structures with a controllable hole density in the channel are useful in understanding the scattering mechanisms limiting mobility of holes confined near to normal ͑Si on SiGe͒ and inverted ͑SiGe on Si͒ interfaces of the Si/SiGe/Si quantum wells, so gating these structures allows one to change the hole sheet density systematically in a single device. MOS gating of undoped Si/SiGe/Si structures 4 and back-gating of normal MD structures 7,8 has been reported to study the transport properties of holes confined at the normal interface. Here we present the low-temperature transport properties of holes at the inverted interface of Si/Si 0.8 Ge 0.2 /Si structures by means of a metal-semiconductor ͑Schottky͒ gate deposited on top of these structures and a Si boron-doped layer beneath the alloy.…”

Enhancement of thermoelectric power factor of MnSi1.7 films by Si addition and modulation doping

“…It is well known that modulation doping can be used to increase the carrier mobility in the well of a quantum‐well structure, and thus reduction of the electrical resistivity as seen from Eq. (3) 16–21. In modulation doping, only the barrier layer (the wide band gap semiconductor, in our case Si) is intentionally doped leaving the neighboring well layer (the narrow band gap semiconductor, in our case MnSi 1.7 ) essentially free of impurities.…”

ENHANCEMENT OF THERMOELECTRIC POWER FACTOR BY A SILICON SPACER IN MODULATION-DOPED Si-HMS-Si

“…7,8 In quantum-well structures, it is well known that modulation doping can be used to increase the carrier mobility in the well. [9][10][11][12][13][14] In modulation doping, only the barrier layer (wide band gap semiconductor, in this case silicon) is intentionally doped, leaving the neighboring well layer (narrow band gap semiconductor, in this case MnSi 1.7 ) essentially free of impurities. Owing to the discontinuity in the valence band at the barrier-well interface, carriers transfer from the bound states of the barrier layer to valence band states in the well layer for a p-type quantum-well structure.…”

“…The introduction of the un-doped spacer is expected to result in further enhancement of carrier mobility. [11][12][13] However, the carrier density decreases with increasing un-doped spacer thickness. It is thus expected that the electrical resistivity decreases with increasing spacer thickness, reaches a minimum value, and then increases.…”