Project Details
Projekt
Tunable Quantum Photoconductor for efficiency-enhanced THz switches (QPC-Switch)
Subject Area
Hardware Systems and Architectures for Information Technology and Artificial Intelligence, Quantum Engineering Systems
Term
from 2015 to 2023
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 276992184
Photoconductive semiconductors have been widely investigated for applications requiring ultrafast optical switching. THz-frequency photoconductors must have both high carrier mobility and short carrier recombination time for optimal efficiency. These two requirements, however, are difficult to simultaneously optimize because short carrier lifetimes in materials usually requires some sort of defect that also degrades the carrier mobility. The goal of the collaborative Quantum Photoconductor (QPC) Switch project has been to decouple the optimization of these two parameters through the judicious use of semiconductor heterostructures, allowing us to separate carrier transport and carrier recombination. We have focused in this collaboration on the use of transition metal (TM) doping of InGaAs/InAlAs heterostructures lattice-matched to InP. The InGaAs system is compatible with telecom-frequency lasers for driving the switch. In prior DFG projects, we have focused first on the use of Fe and Rh. The use of molecular beam epitaxy for TM-doped semiconductor photoconductive switches was first demonstrated within this collaboration. Our collaborative investigation of TM-doped InGaAs has shown that Fe, Rh and Ru act as deep acceptors in InGaAs. Such deep levels can compensate the natural n-type conductivity found in InGaAs prepared epitaxially by MBE. We have recently shown that Rh, like Fe, forms clusters at elevated concentrations. Such Fe- or Rh-clusters are no longer simple point defects and the compensation effect of deep acceptors saturates. At the same time, we have also found that Ru appears to incorporate as an isolated deep acceptor to much higher Ru concentrations, perhaps due to the lower surface mobility during epitaxy. This property leads to higher deep acceptor concentrations in InGaAs using Ru than with the other transition metals, and allows us to completely compensate the n-type background in InGaAs using Ru. Thus, although QPC structures doped with Fe or Rh have shown excellent room-temperature Hall mobilities and sub-picosecond lifetimes, the use of Fe and Rh is not consistent with ultra-low dark conductivity due to clustering. Thus, a remaining challenge lies in reducing further the background carrier concentration. The solution we propose, and that we would like to explore in the proposed extension project, is to combine high-concentration clustered Rh or Fe with non-clustered Ru to achieve simultaneously ultrashort lifetimes, high mobility, and low dark carrier concentration. Preliminary results indicate that the combination of Rh and Ru can result in significant improvements in ultrafast, TM-doped photoconductors for THz emitters and receivers. The goal of the project prolongation is to investigate the dual-doping approach in depth and to realize the full potential of TM-doped InGaAs material system for application as THz antennas.
DFG Programme
Research Grants
