Temperature Dependence of Alternating Current Impedance in n -Type Si/B-Doped p -Type Ultrananocrystalline Diamond Heterojunctions Produced Through Pulsed Laser Deposition.

In the present research, heterojunctions comprised of n-type Si wafer substrates and B-doped p-type ultrananocrystalline diamond/hydrogenated amorphous carbon composite films were produced successfully by using pulsed laser deposition. Their alternating current impedance characteristics, under various frequencies, were measured and studied as a function of temperature in the range 200 to 400 K. Both the real (Z') and imaginary (Z ") parts of the complex impedance were temperature dependent. It was apparent that the Z "-Z' curve for all temperatures exhibited single semicircles. The center of these semicircles was below the Z' axis. With temperature increment, the diameter of the semicircles decreased. The characteristics of the semicircular curve indicated that the parallel resistance (R-p) and constant phase element (CPE) in parallel combination with the series resistance (R-s) should be appropriate for the equivalent electrical circuit model for the produced heterojunctions. Through simulation, the value of R-s at 200 K was found to be 5.04 x 10(3) Omega, and fell to 252.05 Omega at 400 K. Also, the value of R-p was 1.34 x 10(7) Omega at 200 K and decreased to 3.37 x 10(5) Omega at 400 K. Moreover, the value of CPE at 200 K was 95.91 x 10(-12) F with a deviation from the standard (n) value of 0.90 and rose slightly to 115.60 x 10(-12) F with an n value of 0.98 at 400 K.