THz intersubband electroluminescence from n-type Ge/SiGe quantum cascade structures

TL;DR

This paper demonstrates terahertz electroluminescence from n-type Ge/SiGe quantum cascade structures with emissions at 3.4 and 4.9 THz, analyzed through experiments and theoretical modeling, showing lower efficiency than GaAs-based devices.

Contribution

First demonstration of THz electroluminescence from Ge/SiGe quantum cascade structures with detailed spectral analysis and theoretical modeling.

Findings

Emission centered at 3.4 and 4.9 THz with 0.2% line broadening

Spectral features well described by non-equilibrium Green's function calculations

Emission efficiency an order of magnitude lower than GaAs/AlGaAs structures

Abstract

We report electroluminescence originating from L-valley transitions in n-type Ge/Si$_{0.15}$Ge$_{0.85}$ quantum cascade structures centered at 3.4 and 4.9 THz with a line broadening of $\Delta f/f \approx 0.2$. Three strain-compensated heterostructures, grown on a Si substrate by ultrahigh vacuum chemical vapor deposition, have been investigated. The design is based on a single quantum well active region employing a vertical optical transition and the observed spectral features are well described by non-equilibrium Green's function calculations. The presence of two peaks highlights a suboptimal injection in the upper state of the radiative transition. Comparison of the electroluminescence spectra with similar GaAs/AlGaAs structure yields one order of magnitude lower emission efficiency.