We observed the polarity-dependent thermionic emission (TE) and conversion characteristics of n-type GaN-based cathodes with Cs adsorbed on their surfaces. TE current from the surface of an n-GaN sample with N-polarity was 0.18 mA at an applied anode voltage of 30 V at 500 °C. This TE current was markedly higher than that of a sample with Ga-polarity, which had a corresponding TE current of 0.063 mA. We consider the N-polarity with spontaneous polarization to be the cause of the increase in electron density at the Cs/n-GaN interface. TE current was also detected from both samples with Ga- and N-polarity even when the applied anode voltage was 0 V or lower, indicating the presence of thermionic conversion characteristics. From the viewpoint of a thermionic converter, the electromotive force for TE was 0.12 V higher when using the N-polarity n-GaN cathode compared with the Ga-polarity cathode. The short-circuit currents at 500 °C were 4.8 and 0.97 μA for the sample with N-polarity and the one with Ga-polarity, respectively.

中文翻译：

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热离子发射的表面极性依赖性和n型GaN阴极的转换特性

我们观察到Cs吸附在其表面上的n型GaN基阴极的极性依赖性热电子发射（TE）和转换特性。在500°C下施加30 V阳极电压时，来自具有N极性的n-GaN样品表面的TE电流为0.18 mA。该TE电流明显高于具有Ga极性的样品的TE电流，该样品的相应TE电流为0.063 mA。我们认为具有自发极化的N极性是Cs / n-GaN界面电子密度增加的原因。即使在施加的阳极电压为0 V或更低时，也从具有Ga和N极性的两个样品中也检测到TE电流，表明存在热电子转换特性。从热电子转换器的角度来看，TE的电动势为0。与使用Ga极性的阴极相比，使用N极性n-GaN阴极时高12V。500°C时的短路电流为4.8和0.97 μ一种用于与N极分别与样品和一个与Ga的极性。