Charge Carrier Transport Analysis in Radial and Axial Charge-Separating Junctions of III/V Semiconductor Nanowires

• Applicants: Professor Dr. Thomas Hannappel; Dr.-Ing. Werner Prost
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 428769263

• Final Report Year: 2023

Final Report Abstract

About 20 years ago, semiconductor nanowires opened the door to a new form of miniaturization of electronic and optoelectronic components. The epitaxy of crystalline, planar and modulation-doped semiconductor layers, which enabled material control on the atomic scale in the direction of growth, was extended into the third dimension. The wires, which are epitaxially grown in a controlled manner in 3D, reduce the amount of material used on the active component. Since the lattice of the nanometer-thin wires behaves elastically, the simple crystal relaxation of the thin wires greatly extends the limits of material combination in crystalline semiconductor heterostructures. Despite these great advantages, it has not yet been possible to commercially establish nanowire-based components on the market, especially in the area of modulation-doped pn components such as bipolar transistors, solar cells, LEDs, and lasers. One of the main reasons was the problem of high leakage currents in charge-separating pn junctions. This project aims precisely at this deficit with the comprehensive aim of identifying the physical mechanisms, localizing them in the nanowire and demonstrating approaches to suppress them. The identification of the physical mechanisms was advanced through a combination of experimental studies and physical simulation in the GaAs/GaInP system. It became clear that the Shockley-Read-Hall model, which perfectly describes pn-junctions from optimized pn-junctions in semiconductor layers, is not sufficient. The combination of experimental and simulation studies on the pn junction led to the finding that tunnel-assisted recombination mechanisms dominate the leakage current behavior in the nanowire pn junction. In the case of vertical nanowires, which are still attached to the growth substrate, an additional leakage path via the substrate was identified by 4-point probe measurements using a multi-tip scanning tunneling microscope (MT-STM). This is of particular relevance for applications of vertical core-shell nanowires, e.g. for nanowire solar cells. Also, the contact between the MT-STM tips and the nanowires was analyzed in detail, and it was shown that charging and discharging takes place which leads to hysteresis and had to be considered in the electrical characterization of nanowires. A reduction in the leakage current by 5-6 orders of magnitude led to the development of nanowire-based devices, in particular a detector for hard X-rays and heterojunction bipolar transistor with active current amplification.

Publications

• n‐Doped InGaP Nanowire Shells in GaAs/InGaP Core–Shell p–n Junctions. physica status solidi (b), 257(2).
  Liborius, Lisa; Bieniek, Jan; Nägelein, Andreas; Tegude, Franz-Josef; Prost, Werner; Hannappel, Thomas; Poloczek, Artur & Weimann, Nils
  
• Hot electrons in a nanowire hard X-ray detector. Nature Communications, 11(1).
  Zapf, Maximilian; Ritzer, Maurizio; Liborius, Lisa; Johannes, Andreas; Hafermann, Martin; Schönherr, Sven; Segura-Ruiz, Jaime; Martínez-Criado, Gema; Prost, Werner & Ronning, Carsten
  
• Tunneling‐Related Leakage Currents in Coaxial GaAs/InGaP Nanowire Heterojunction Bipolar Transistors. physica status solidi (b), 258(2).
  Liborius, Lisa; Bieniek, Jan; Possberg, Alexander; Tegude, Franz-Josef; Prost, Werner; Poloczek, Artur & Weimann, Nils
  
• Leakage Current Suppression in Coaxial GaAs/InGaP Nanowire pn- Heterojunctions, NRW Nano Konferenz 2021.
  L. Liborius et al.
  
• Multi-probe electrical characterization of freestanding core-multishell GaAs-GaInP nanowire structures, EMRS 2021
  J. Koch et al.
  
• Polarity-controlled AlN/Si templates by in situ oxide desorption for variably arrayed MOVPE-GaN nanowires. Journal of Crystal Growth, 566-567, 126162.
  Häuser, Patrick; Blumberg, Christian; Liborius, Lisa; Prost, Werner & Weimann, Nils
  
• Spatially high-resolution I-V characterization of freestanding core-shell nanowires, ACCGE 2021
  J. Koch et al.
  
• Electrical Properties of the Base‐Substrate Junction in Freestanding Core‐Shell Nanowires. Advanced Materials Interfaces, 9(30).
  Koch, Juliane; Liborius, Lisa; Kleinschmidt, Peter; Weimann, Nils; Prost, Werner & Hannappel, Thomas
  
• Influence of the measuring tip-to-semiconductor contact on the overall electrical characterization of nanowire structures, EMRS 2022
  J. Koch et al.
  
• Spatially resolved multi-probe electrical characterization of GaAs-based nanowire structures, ICMOVPE 2022.
  J. Koch et al.