Highly Sensitive UV Detection Mechanism in AlGaN/GaN HEMTs

AlGaN/GaN high electron mobility transistors are demonstrated with a very high dc responsivity ( ~ 4.3×10⁷ A/W at ~ 5×10^-11 W) to UV light. The gain mechanisms in the device are shown to be due to a photo voltage effect in both the AlGaN barrier layer and the GaN buffer layer. In the case of absorption in the barrier layer, trapped surface electrons, which are a characteristic of unpassivated devices, are neutralized by the movement of holes toward the surface, creating a net positive-gate bias. The photovoltage generated in the GaN buffer region is due to photocarrier separation and acts as a positive back-gate bias. The dc photocurrent response and responsivity are very strong functions of intensity that are explained by the proposed mechanisms, with absorption in the GaN buffer region dominating.