Three-dimensional imaging of beam-induced biasing of InP/GaInP tunnel diodes

TL;DR

This study used electron holographic tomography to visualize and analyze the 3D morphology and electrostatic potential of InP/GaInP nanowire tunnel diodes, revealing effects of electron beam charging and biasing on their electrical properties.

Contribution

It provides the first 3D reconstructions of the electrostatic potential in InP/GaInP tunnel diodes and investigates beam-induced biasing effects on their electrical characteristics.

Findings

Confirmed short depletion widths (~21 nm) in both diodes.

Measured different built-in potentials (1.0 V and 0.4 V) from expected values.

Identified beam-induced charging effects affecting diode behavior.

Abstract

Electron Holographic Tomography was used to obtain 3-dimensional reconstructions of the morphology and electrostatic potential gradient of axial GaInP/InP nanowire tunnel diodes. Crystal growth was carried out in two opposite directions: GaInP:Zn/InP:S and InP:Sn/GaInP:Zn, using Zn as the p-type dopant in the GaInP, but with changes to the n-type dopant (S or Sn) in the InP. Secondary electron and electron beam induced current images obtained using scanning electron microscopy indicated the presence of p-n junctions in both cases and current-voltage characteristics measured via lithographic contacts showed the negative differential resistance, characteristic of band-to-band tunneling, for both diodes. EHT measurements confirmed a short depletion width in both cases ($21 \pm 3$ nm), but different built-in potentials, $V_{bi}$, of 1.0 V for the p-type (Zn) to n-type (S) transition, and 0.4 V for both were lower than the expected 1.5 V for these junctions, if degenerately-doped. Charging induced by the electron beam was evident in phase images which showed non-linearity in the surrounding vacuum, most severe in the case of the nanowire grounded at the \emph{p}-type Au contact. We attribute their lower $V_{bi}$ to asymmetric secondary electron emission, beam-induced current biasing and poor grounding contacts.