Lab exchange grant: Multimodal micro-spectroscopy characterisation of semiconductors

Kimberly Nicholson PhD student at Cardiff University, was awarded an M4QN laboratory exchange grant to visit Professor Robert Martin at the University of Strathclyde.

The purpose of the visit

Kimberley writes: “During my laboratory exchange, I was able to apply nanoscale optical and electrical characterisation techniques of hyperspectral-cathodoluminescence (CL) and electron beam-induced current (EBIC) on varying wideband gap materials and devices. We had previously investigated III-nitrides on sapphire using electron channelling contrast imaging (ECCI) to image the threading dislocation density present within a region of interest and looked at this region using photoluminescence with HBT to correlate the threading dislocations with the possibility of colour centres. However, due to the difference in resolution it was difficult to correlate the colour centres with the threading dislocation and so we implemented hyperspectral-CL during the exchange to investigate the emission from this sample. Additionally, we investigated the active region of a degraded wide-bandgap laser compared to a fresh device to understand the changes of the active region using EBIC, where results from this have formed an abstract for an international conference. This exchange has given me an opportunity to understand hyperspectral-CL at an in-depth level with thanks Dr. Paul Roberts and Prof. Robert Martin. I was also given the opportunity learn how to analyse such complex results, using home-built software, something I did not have access to before. The knowledge I have gained from this laboratory exchange has laid a strong foundation, allowing me to expand and share my experiences to my colleagues where our own hyperspectral-CL will be live in summer 2025, the preliminary results from this exchange allowed us to write an abstract for CLEBIC, a conference for CL and EBIC users.”

Benefits to the UK materials and quantum community

Recently, III-nitrides specifically, gallium nitride (GaN) and aluminium nitride (AlN) have gained numerous attention, as single photon emitters (SPE) have been found at room-temperatures. SPE are an integral part of quantum computing but the origin of SPE remains unsure. Therefore, this laboratory exchange hoped to answer the following, “Are extended defects in III-nitrides the prime source of colour centres and their role in determining the electrical and optical properties relevant for next-generation quantum light sources?” This research aligns with one of M4QNs main aims: “characterisation and properties of colour centres, a key activity within the solid-state defect group”. During the exchange they investigated wurtzite GaN on sapphire which they had completed preliminary results such as electron channelling contrast imaging (ECCI) to examine the threading dislocation present within a region and correlated with photoluminescence with BHT to check for colour centres. As the resolution between the electron and light-based microscopy, they were unable to correlate origins of colour centres. This is where the exchange was of great benefit as they were able to use University of Strathclyde’s hyperspectral-CL to investigate the light emission of the sample. Though this did not provide a firm answer, it very much began the foundations of answering this vital question.

Visit outcomes

The visit started a new collaboration between Kimberley and Dr Paul Edwards and Prof. Robert Martin at the University of Strathclyde. The preliminary results of the visit have been used for successfully submitted an abstract for CLEBIC conference taking place in Glasgow in April 2025. Kimberley says: “I have been taught varying sample preparations, best practice for measuring/investigating the active region of devices using EBIC as well as hyperspectral-CL. Moreover, I have been taught and given home-built software used for analysing these complex data set which would have otherwise been unavailable to myself. We are looking at future visits in the summer as well as an international conference.”