Epitaxial Sb-doped SnO2 and Sn-doped In2O3 transparent conducting oxide contacts on GaN-based light emitting diodes

• Plasma-assisted molecular beam epitaxy of SnO2:Sb (ATO) and In2O3:Sn (ITO) contacts
• Working light emitting diodes processed with the ATO contact on the top p-GaN layer
• Low growth temperature ensures low contact resistance (limiting interface reaction).
• ITO showed significantly better structural and transport properties than ATO.
• ATO showed higher optical transmission at short wavelengths than ITO.

We demonstrate the growth of epitaxial (100)-oriented, rutile Sb-doped SnO2 (ATO) and (111)-oriented, cubic Sn-doped In2O3 (ITO) transparent conducting oxide (TCO) contacts on top of an InGaN/GaN(0001) light emitting diode (LED) by plasma-assisted molecular beam epitaxy (PAMBE). Both oxides form rotational domains. The in-plane epitaxial alignment of the two ITO(111) rotational domains to the GaN(0001) was: GaN [21-10]|| ITODomain1[‐ 211]|| ITODomain2[‐ 1‐12]. A growth temperature as low as 600 °C was necessary to realize a low contact resistance between ATO and the top p-GaN layer of the LED but resulted in non-optimal resistivity (3.4 × 10− 3 Ω cm) of the ATO. The current–voltage characteristics of a processed LED, however, were comparable to that of a reference LED with a standard electron-beam evaporated ITO top contact. At short wavelengths, the optical absorption of ATO was lower than that of ITO, which is beneficial even for blue LEDs. Higher PAMBE growth temperatures resulted in lower resistive ATO but higher contact resistance to the GaN, likely by the formation of an insulating Ga2O3 interface layer. The ITO contact grown by PAMBE at 600 °C showed extremely low resistivity (10− 4 Ω cm) and high crystalline and morphological quality. These proof-of-principle results may lead to the development of epitaxial TCO contacts with low resistivity, well-defined interfaces to the p-GaN to help minimize contact losses, and enable further epitaxy on top of the TCO.