The discovery of a superhard P-type transparent semiconductor: Al_2.69B₅₀

Superhard semiconductors have been long sought after for electronic device applications enduring extreme conditions, such as astronautics, due to their intrinsic toughness, high thermal and chemical stability. Here, we report the superhard p-type semiconductor Al2.69B50 single crystal with the determined Vickers hardness of ∼40.5 GPa under the load of 0.49 N, which is one of the hardest semiconductor compounds that have been ever found. With the direct band gap of 2.3 eV, Al2.69B50 exhibits excellent optical transmittance (>90%), covering the visible range from 459 nm to 760 nm and part of the infrared range, and also shows the high intensity of the photon emission in the visible light. Al2.69B50 is very stable, thermally and chemically, with an ultra-low density of ∼2.52 g cm-3, allowing for further extension of its applications. Such an assembly of various excellent properties within one material has great implication for high power electronic design and applications.