Synthesis of c-axis-oriented MgB₂ thin films and the Hall effect

We have synthesized c-axis-oriented MgB₂ thin films on (1 1̄ 0 2) Al₂O₃ substrates by using a pulsed laser deposition technique and have measured the longitudinal and the Hall resistivites in the ab-plane direction. The as-grown thin films show T_c of 39.2 K with a sharp transition width of ∼0.15 K. In the normal state, the Hall coefficient (R_H) behaves as R_H ∼ T with increasing temperature (T) up to 130 K and then deviates from that linear T-dependence at higher temperatures. The T² dependence of the cotangent of the Hall angle is only observed above 130 K. We estimate the absolute value of the hole density to be about two orders of magnitude higher than that of YBa₂Cu₃O₇.