(Invited) Imaging and Measuring Electronic Materials

Photoemission (PES) has been an essential metrology in the field of materials physics for over 30 years. The electronic band structure of a solid is a fundamental property which defines how a material will be used and integrated into device form. Topographic features and defects can impact electronic structure, therefore influence extrinsic properties when integrated in device form. Developing metrology that is sensitive to electronic properties at these length scales is desired. Here, we apply lab-based photoemission electron microscopy (PEEM) to gain insight in key structure – function relationships. Controlling doping during growth of semiconductors is critical as it has impact on device engineering – whether to form components in logical circuits or regions for Ohmic contact formation. For some semiconductor nanowires (NW), the doping density is varied along the long axis of the NW and knowing where the transition and its strength between doping regimes is important for device engineers. Here, we have imaged GaN NW grown with n-doped and n++-doped regions of approximately 6 μm in length and 200 nm in diameter that have been dispersed on a silicon substrate. Using a deep ultraviolet photon source, we observe an inflected change in the contrast along the long axis of the NWs (about 2 μm from one end) which we attribute to the n-n++ interface. This inflection is about 100 nm wide, and provides insight into the space-charge region formed at this electronic interface. We will also present on expanding our lab-based PEEM capability with integration to a tunable laser-based deep UV system (80 MHz, 140 fs). This added capability will provide additional imaging sensitivity to polar semiconductors such as III-nitrides. We will present some initial results with this system currently being commissioned on device-grade GaN and β-Ga2O3.