With the development of information and communication technology, conventional semiconductors such as Si and GaAs cannot satisfy the requirement of high‐frequency and high‐power electronic devices. By contrast, diamond film has been considered to be a potential material alternative due to the highest Johnson and Keyse figures of merit. In this paper, H‐terminated polycrystalline diamond films with different quality were prepared by DC arc jet CVD through adjusting the deposition conditions. The conductive behaviour of p‐type channel on H‐terminated diamond surface was compared and analyzed based on the N‐related impurity and spontaneous polarization model. After that, MESFETs (metal‐semi‐conductor field effect transistor) were fabricated on H‐terminated diamond and the radio frequency (RF) performance was evaluated. The cut off frequency (fT) of 11 GHz and the maximum oscillation frequency (fmax) of 18.5 GHz for MESFET in our situation were obtained. It was found that equivalent circuit elements were lower or comparable with the reported values for the FETs with the highest fT and fmax except the gate capacitance, which indicates that the carrier mobility should be improved further for high‐frequency devices application. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Diamond-based semiconductor with high electrical conductivity is a key point in diamond device development. In this paper, a thin single-crystal diamond layer of high quality was epitaxially grown on a commercial tool-grade diamond seed by incorporating active O atoms from the typical growth environment. Subsequently the Htermination density was enhanced on the diamond surface by exposure to the pure hydrogen plasma, and the surface conductivity of H-terminated diamond was analyzed in detail. The thin epitaxial layers on the high pressure high temperature (HPHT) diamond seeds show lower resistance than the ones on the chemical vapor deposition (CVD) diamond seeds, which could be comparable with the lowest values reported. After the thin diamond layers were grown with and without addition of O 2 , the carrier mobility in the conductive channel increase to almost 80 cm 2 •V-1 •s-1 under O 2 contained condition, much higher than those without O 2 incorporation. The ionization scattering is dominant to the carrier mobility compared with the surface scattering. The higher carrier mobility is attributed to the lower impurity density in the epitaxial layer, which is because the active O atoms could purify the epitaxial layer by removing or reducing Si and N related impurities.

The ultrathin InAlN/GaN heterostructure with 3 nm thickness was grown by metal organic chemical vapor deposition, and a room‐temperature mobility of 2175 cm2/V · s at sheet density of 1.39 × 1013 cm−2 was achieved. Excellent crystalline and structural quality of the ultrathin InAlN/GaN heterostructure was revealed by transmission electron microscopy and atom force microscopy. The double periodicity of the Shubnikov–de Haas (SdH) oscillation was observed in the magnetoresistance measurements, and the energy separation between the two subbands was determined as 116 meV. It was found that the smaller interface electric field for the ultrathin InAlN/GaN was responsible for the smaller energy separations, which facilitated the occupation of the second subband.