Sumitomo Electric developed a gallium nitride high electron mobility transistor (GaN-HEMT). GaN-HEMTs are widely used in high-frequency amplifier applications, including 5G. In the future post-5G era, the transistors used in communication devices will be required to support higher power and higher frequencies for an increased volume of data transmission.

Conventionally, Ga-polar (0001 orientation) GaN has been widely used. Along with the demand for further higher power and higher frequencies, however, attention is being focused on the improvement of characteristics with N-polarity (000-1 orientation) (the crystal orientation is different from that of the Ga-polarity), which enables an inverted HEMT structure that increases the degree of freedom in device design and can reduce leakage current. Meanwhile, N-polar crystals have the problem of being prone to irregularities caused by abnormal growth called hillocks. In addition, in terms of device design, the realization of an inverted HEMT structure required the development of a high-quality gate insulating layer that would serve as a barrier against the gate electrode in place of the conventional semiconductor barrier layer.

Therefore, Sumitomo Electric has utilized its years of experience in crystal growth technology to realize high-quality N-polar crystals without hillocks. In addition, by applying a type of hafnium (Hf)-based heat-resistant and high-dielectric material to the challenging gate insulating layer, the company completed an N-polar crystal transistor incorporating a high-dielectric material and achieved excellent high-frequency characteristics.

This achievement is the result of the Research and Development Project for Strengthening Post-5G Telecommunication System Infrastructure, commissioned by the New Energy and Industrial Technology Development Organization (NEDO).