Current Transport Mechanism Of Ingan Metal-insulator-semiconductor Photodetectors And Self-assembly Of Metal Nanoparticles

The band gap of GaN-based semiconductor is continuously adjustable from0.7eV to6.2eV, which is corresponding to wavelength range from near-infrared to ultraviolet. The detectors based GaN material is expected to be widely used in fire, missile warning, and other fields. In recent years people have been working on InGaN and AlGaN materials with high In or Al content, but it is difficult to get high quality crystal due to high density of defects in materials. Devices prepared by traditional processes do not meet the requirement. So we should develop new processes. Plasma technology has been widely used in the light emitting diode (LED), and the technology also can be used to improve the performances of the photodetector. The application of metal nanoparticle in the photodetector has attracted wide attention.In order to reduce the influence of the high density of surface states on the InGaN photodetectors, we employed the metal-insulator-semiconductor (MIS) structure to improve Schottky barrier and reduce leakage current. Moreover, the metal nanoparticles were fabricated through self-assembled method. The main research results are as follows:1) The current transport mechanisms and photoelectric responsivity of InGaN MIS photodetectors with Si3N4and Al2O3insulating layers deposited by plasma-enhanced chemical vapor deposition and by atomic layer deposition, respectively, were investigated. The results show that the space-charge-limited current (SCLC) mechanism is a dominant leakage conduction mechanism in the InGaN MIS photodetectors. The SCLC mechanism is mediated by an exponential trap distribution, and a bi-directional Fowler-Nordheim tunneling effect is observed in the metal-Si3N4-InGaN photodetector. The metal-Si3N4-InGaN photodetector has a far lower photoelectric responsivity than the metal-A12O3-InGaN photodetector. In the Si3N4bulk, a higher trap-state density exists with an exponential distribution, and therefore the electrons that are injected from the metal under reverse bias are easier to capture by these acceptor-like traps, which leads to the formation of a trapped electron space charge. These trapped electrons act as hole traps and they tend to capture the photogenerated free holes from the InGaN semiconductor. Therefore, this trapping process increases the probability of the recombination of photogenerated carriers in the bulk of the dielectrics and at the interface of the dielectric-InGaN and hence decreases the photoelectric responsivity.2) Nanoparticles were prepared by self-assembly with three different metal thin films of Al, Au and Ni. The studies found that the higher annealing temperature and the shorter annealing time, the larger metal nanoparticles. In addition, the particle size is related with the metal itself. The particle size of Ni is biggest whilst the particle size of Al is smallest under the same fabricating conditions. XPS electron spectroscopy results show that the interface reaction between the metal particles and AlGaN surface happened after annealing and the new intermetallic compound was generated.3) Then a nanorod structure is prepared by etching AlGaN surface using metal nanoparticles as template. The result of PL measurement shows that the luminous intensity of nanorod structural p-AlGaN increases several orders of magnitude and be further enhanced after the cleaning of KOH solution.