Temperature dependence of two-dimensional hole gas on hydrogen-terminated diamond surface

The two-dimensional hole gas (2DHG) at hydrogen-terminated diamond (H-diamond) surface has been widely used in the development of diamond-based electronics. However, the carrier transport behaviors of 2DHG are still poorly understood due to the difficulty in controlling surface adsorbates on H-diamond. In this work, the temperature dependence of the electrical properties of 2DHG on H-diamond was investigated through Hall effect measurements before and after thermal annealing. The results revealed that the establishment of 2DHG equilibrium state was closely related to surface adsorbates, and temperature-induced thermal desorption of adsorbates would lead to a decrease in carrier concentration and an enhancement of mobility on H-diamond. Based on this observation, the carrier mobility of 2DHG (at 300 K) was improved from 170 to 340 cm2 V-1 s-1 after thermal annealing to 400 K. Moreover, with thermal desorption of adsorbates, the activation energy of conductance exhibited an increasing tendency, and the carrier concentration became more dependent on temperature, which can be well explained by percolation theory. A dynamic equilibrium process was also proposed to illustrate the influence of surface adsorbate on carrier concentration and mobility of 2DHG, which provides a feasible method to regulate carrier mobility and concentration on H-diamond surface.