This study examines terahertz radiation from a series of In0.52 Al0.48 As and GaAs surface-intrinsic- N+ structures (SI N+) with surface-intrinsic layers of various thicknesses. The built-in electric fields in the SI N+ structures are used as the bias. Experimental results indicate that the amplitudes of the THz emission are independent of the built-in electric fields in the emitters when the built-in electric fields exceed the corresponding critical electric fields of the semiconductors. In contrast, the amplitudes of the THz emission are proportional to the thickness of the intrinsic layer and, therefore, the number of photo-excited charged carriers.
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