Transformation of germanium to fluogermanates

TL;DR

This study demonstrates the transformation of germanium surfaces into germanium fluorides and oxides using HF and HNO3 vapors, revealing detailed structural, vibrational, and electronic properties of the resulting layers.

Contribution

It introduces a novel vapor-phase chemical process to create germanate layers on germanium, with comprehensive analysis of their structure and electronic characteristics.

Findings

Formation of germanate polycrystalline layers with <101> orientation

Presence of N-H, Ge-F vibrational modes confirmed by vibrational analysis

Surface emits yellow photoluminescence at room temperature

Abstract

The surface of a single crystal Germanium wafer was transformed to crystals of germanium fluorides and oxides upon exposure to a vapor of HF and HNO3 chemical mixture. Structure analysis indicate that the transformation results in a germanate polycrystalline layer consisting of germanium oxide and ammonium fluogermanate with a preferential crystal growth orientation in <101> direction. Local vibrational mode analysis confirms the presence of N-H and Ge-F vibrational modes in addition to Ge-O stretching modes. Energy dispersive studies reveal the presence of hexagonal {\alpha}-phase GeO2 crystal clusters and ammonium fluogermanates around these clusters in addition to a surface oxide layer. Electronic band structure as probed by ellipsometry has been associated with the germanium oxide crystals and disorder induced band tailing effects at the interface of the germanate layer and the bulk Ge wafer. The acid vapor exposure causes Ge surface to emit a yellow photoluminescence at room temperature.