III-V nitride semiconductors are attractive materials that can be applied in various optoelectronic devices such as photodetectors (PDs) and light-emitting diodes (LEDs). In fact, nitride-based LEDs are already commercially available and have been extensively used in traffic-light sources and full color display. In addition, nitride-based PDs [1] are also important devices that can be used in various commercial and military applications. Depending on the device structure, nitride-based p-i-n diodes [2], [3], Schottky-barrier PDs [4], and metal–semiconductor–metal (MSM) PDs [5], [6] could all be used to detect blue/UV signals. Among these devices, MSM PDs have an ultralow intrinsic capacitance, and their fabrication process is also compatible with field-effect-transistor (FET)-based electronics. Thus, one can easily integrate MSM PDs with FET-based electronics to realize an optoelectronic integrated circuit (OEIC). These advantages make MSM PDs attractive for practical applications. Although it is easier to fabricate GaN-based MSM PDs, the leakage current of such MSM PDs is very large owing to the large differences in lattice constant and thermal expansion coefficient between the epitaxial layer and the underneath substrate. Previously, such a problem could be overcome by inserting a thin insulating layer, such as , between the metal and the semiconductor underneath [7]–[9]. However, these insulators were all ex-situ deposited, and contamination might occur at the insulator–semiconductor interface. Here, we use an in-situ grown, unactivated Mg-doped GaN cap layer as a semi-insulator to reduce the leakage current. Without activation, it is known that Mg-doped GaN is considered to be highly resistive owing to compensation for residual donors [10]. Hence, we believe this semi-insulator can help to suppress the leakage current.
Abstract:
InGaN-GaN multiquantum-well (MQW) metal-semiconductor-metal (MSM) photodetectors (PDs) with the unactivated Mg-doped GaN cap layer were successfully fabricated. It was fo...Show MoreMetadata
Abstract:
InGaN-GaN multiquantum-well (MQW) metal-semiconductor-metal (MSM) photodetectors (PDs) with the unactivated Mg-doped GaN cap layer were successfully fabricated. It was found that we could achieve a dark current by as much as six orders of magnitude smaller by inserting the unactivated Mg-doped GaN cap layer. For MSM photodetectors with the unactivated Mg-doped GaN cap layer, the responsivity at 380 nm was found to be 0.372 A/W when the device was biased at 5 V. The UV-to-visible rejection ratio was also estimated to be around 1.96 times 103 for the photodetectors with the unactivated Mg-doped GaN cap layer. With a 5-V applied bias, we found that minimum noise equivalent power and normalized detectivity of our PDs were 4.09 times 10-14 W and 1.18 times 1013 cmmiddotHz0.5W-1, respectively. Briefly, incorporating the unactivated Mg-doped GaN layer into the PDs beneficially brings about the suppression of dark current and a corresponding improvement in the device characteristics.
Published in: IEEE Journal of Quantum Electronics ( Volume: 43, Issue: 11, November 2007)