Progress Toward Diamond Power Field‐Effect Transistors

Abstract

Diamond's properties (highest thermal conductivity, high hole & electron mobilities, & high electric breakdown field) predict that diamond field‐effect transistors (FETs) will have superior high‐power high‐frequency performance over FETs formed in other semiconductors. The development of diamond FETs is limited by a lack of quality substrates & the high ionization energy of the primary dopant, boron (B). This high ionization energy results in a resistance too high for FETs. Fortunately, recent developments are addressing these shortcomings. Single‐crystal diamond substrates ≈4 inches have been demonstrated. Further, two approaches address the dopant issue. When the surface of diamond is terminated in H, a surface p‐type conductive layer forms. FETs made using this layer demonstrate competitive high‐frequency performance, though manufacturability of this type of device has yet to be worked out. The second solution to doping uses delta doping by B. A thin <2‐nm layer doped with B at >1020 cm−3 is sandwiched within undoped diamond. This structure mitigates B's high ionization energy by producing an acceptor subband with ≈100% of the B is ionized. Recent reports of delta‐doped diamond have channel resistances suitable for device applications. This article reviews the state of the art for FET and substrate development.