National Science Foundation Sb-doped SnO 2 as a transparent contact on InGaN/GaN LEDs James S. Speck, University of California-Santa Barbara, DMR Outcome UCSB researchers have demonstrated Sb-doped SnO 2 (ATO) epitaxial contacts on GaN- based LEDs with equal performance to Sn-doped In 2 O 3 (ITO) contacts Impact Tin is relatively abundant and low cost compared to Indium ATO should also have better optical transparency than ITO Explanation High performance ATO contacts were realized via optimized epitaxial growth conditions on high performance GaN LED wafers. The ATO resistivity was 3.4x10 -3 Ωcm Fig. (a) optical image of 290×490 µm 2 fabricated LEDs and TLM patterns; (b) the cross-section of the LED structure, (c) I-V curves for InGaN/GaN LEDs fabricated with ITO and ATO contacts

National Science Foundation High quality In 2 O 3 for transparent electronics James S. Speck, University of California-Santa Barbara, DMR Outcome Demonstration of record mobility in In 2 O 3 thin films via MBE on foreign substrates Impact Demonstrates potential In 2 O 3 as a for advanced devices when bulk In 2 O 3 substrates are used for growth. Our partners at the Institue for Crystal Growth (IKZ) in Berlin have now demonstrated bulk In 2 O 3 substrates. Explanation Binary oxides - prepared with high quality and purity - are promising wide bandgap semiconductors for future electron devices. Lower quality and purity forms of these oxides are used as transparent contact for LEDs, displays and solar cells, and as chemical sensors. This work demonstrates how In 2 O 3 can be prepared with high structural [1] and electrical [2] quality. High structural quality, such as a smooth surface, is necessary for most device technologies, whereas high electrical quality (e.g. high mobilities) ensure high device performance. The high material quality allows investigation of intrinsic material properties (doping, transport, optical properties …). [1] O. Bierwagen and J.S. Speck, J. Appl. Phys.107, (2010). [2] O. Bierwagen and J.S. Speck, Appl. Phys. Lett. 97, (2010).

National Science Foundation Materials World Network: Growth and Characterization of Bulk Crystals and Epitaxial Films of Beta-Ga 2 0 3, SnO 2, In and ZnO James S. Speck, University of California-Santa Barbara, DMR Second joint UCSB-Humboldt University-IKZ Focused Workshop Held at IKZ (Adlershof, Berlin, Germany) – October 13-14, 2011 The second focused workshop on semiconducting oxides was held at IKZ in October Participants came from the German and US project partners UCSB (Jim Speck’s group), Institute of Crystal Growth, Berlin (IKZ), and Humboldt University, Berlin and from several other institutes and universities. The fifteen contributions by professors, postdocs, and graduate students dealt with the preparation (both, bulk and thin films) and the properties (theory and experiment) of semiconducting oxides. The moderate number of contributions and participants allowed for in-depth discussion in an informal atmosphere, which strengthened existing- and established new collaborations among the participants.

National Science Foundation Studies of Surface Fermi Level in In 2 O 3 and SnO 2 James S. Speck, University of California-Santa Barbara, DMR Surface Fermi Level from XPS (left) panels: In 2 O 3 as-grown and after plasma oxidation (right) panel: SnO 2 doped: Sb; undoped; In Outcome Demonstration control of surface Fermi level in semiconducting oxides: In 2 O 3 and SnO 2 Impact Demonstrates that the surface accumulation layer can be controlled via light surface damage or bulk doping Explanation Binary oxides - prepared with high quality and purity - are promising wide bandgap semiconductors for future electron devices. One common feature of wide bandgap semiconducting oxides is the propensity for a surface electron accumulation layer – SEAL (also responsible for gas and liquid sensing properties) This work demonstrates how the SEAL in In 2 O 3 can be eliminated with light plasma treatments [1] and how the SEAL in SnO 2 can be controlled with bulk doping [2]. These results come from careful XPS studies at UCSB and NIMS (at Spring8) on UCSB MBE-grown semiconducting oxides. [1] O. Bierwagen et al., Appl. Phys.Lett. 98, (2011). [2] T. Nagata et al., Appl. Phys. Lett. 98, (2011).