Terahertz spectroscopy of an electron-hole bilayer system in AlN/GaN/AlN quantum wells

TL;DR

This study uses terahertz spectroscopy to analyze the transport dynamics of spatially separated electron-hole layers in AlN/GaN/AlN quantum wells, revealing distinct spectral signatures and transport properties.

Contribution

It demonstrates the effectiveness of terahertz spectroscopy in characterizing bilayer charge systems with differing transport behaviors in III-Nitride quantum wells.

Findings

Distinct spectral signatures for electron and hole layers at terahertz frequencies

Extraction of individual conductivity contributions and scattering rates

Identification of defect effects on charge transport

Abstract

We describe studies on the nanoscale transport dynamics of carriers in strained AlN/GaN/AlN quantum wells: an electron-hole bilayer charge system with large difference in transport properties between the two charge layers. From electronic band diagram analysis, the presence of spatially separated two-dimensional electron and hole charge layers is predicted at opposite interfaces. Since these charge layers exhibit distinct spectral signatures at terahertz frequencies, a combination of terahertz and far-infrared spectroscopy enables us to extract (a) individual contributions to the total conductivity, as well as (b) effective scattering rates for charge-carriers in each layer. Furthermore, by comparing direct-current and terahertz extracted conductivity levels, we are able to determine the extent to which structural defects affect charge transport. Our results evidence that (i) a non-unity Hall-factor and (ii) the considerable contribution of holes to the overall conductivity, lead to a lower apparent mobility in Hall-effect measurements. Overall, our work demonstrates that terahertz spectroscopy is a suitable technique for the study of bilayer charge systems with large differences in transport properties between layers, such as quantum wells in III-Nitride semiconductors.