Deep Level In Gan Materials

GaN is considered as one of the typical representatives of the third generationsemiconductors for its eminent properties and great applications. In recent years, somerelative fields have attracted more and more researchers' attention. GaN-based materials have potential applications in both microelectronic and optoelectronicdevices, due to their bandgap ranging from visible light to UV and excellent thermal andchemical stability.GaN, AlN and AlxGa1-xN belong to a same sort of wide-bandgap semiconductors. Thebandwith of GaN is 3.4eV at room temperature, and the bandwith of AlN even reachs 6.2eVat room temperature. One of the important factors which determine the working temperatureof devices is the bandwide of this material. Thus, the working temperature of GaN is muchhigher than that of Si and GaAs devices. Theoretical calculation suggested that the highesteffective working temperature of GaN is higher than 900 oC(4). And experiment hadindicated that the AlxGa1-xN/GaN HFET has a good microwave amplify performance at 500oC.GaN is a kind of semiconductor with wide (3.4eV) and direct band-gap, which makes itentrenched itself in the application of short-wave photoelectric devices. GaN and its relatedalloys, who have the continuous and adjustable band-gaps from 1.6eV(InN) to 6.2eV(AlN),are eligible materials to obtain the luminescence of visible light and ultraviolet, blue andgreen light have been manufactured for commercial purpose. And the investigation toGaN-based LDs and detectors are now in the ascendant. For its wider band gap, GaN LDshave shorter wavelength, which can enhance the storage density of LD memory greatly.The research of GaN has a history of tens of years. In this area, the biggest problemplaguing researcher is that the high defect density in the GaN material due to the heteroepitaxial growth. These defects degrade the performance of GaN based devices. There aremany manifestations of this defect. To characterize these defects, we adopt some measuringand analysis methods, such as the photoluminescence (PL), double crystal X ray diffraction(DCXRD), persistent photoconductivity (PPC), optical quenching (OQ), photovoltage (PV)and so on. Following is the summary of this thesis:1 PPC and recombination mechanism were investigated in an intrinsic GaN at roomtemperature with incident photon wavelength from 360nm-377nm. Experimental resultsreveal two main persistent features: aquickly recombination mechanism result in the PPCdecay magnitude increasing with the incident wavelength;and a slower one, which dose notaffect the decay magnitude of photocurrent when the incident wavelength changes. Aphysical model is proposed based on the two recombination mechanisms the formermechanism may be related to the capture of conduction band electrons by deep electron traps,and the latter is due to the recombination of electrons with holes trapped in hole traps.2 We had studied the minority diffusion length of n-type GaN films grown bymetalorganic chemical vapor deposition (MOCVD) through the measurements of surfacephotovoltaic spectra. We find that minority carrier diffusion length of undoped n-type GaN ismuch larger than that in lightly Si-doped GaN. However, data suggested that the dislocationand electron concentration appear not to be responsible to the minority carries diffusionlength. It is suggested that the Si doping plays an important role in decreasing the minoritycarrier diffusion length.3 The Persistent Photoconductivity (PPC) phenomena in n-type GaN Films grown bymetalorganic chemical vapor deposition (MOCVD) have been studied. After using sometesting and analysis methods, such as the double crystal X-ray diffraction (DCXRD), thephotoluminescence (PL) spectra, etc, it is found that the most likely issue which influencesPPC in n-type GaN is not dislocations and yellow band (YB), but the doping level of Si.4 The study on the optical quenching phenomenon in Si doped and Mg doped GaNsamples. There is extremely different phenomenon in these two kinds of samples. Whenadding red light to the sample to test the photocurrent (PC), the PC in n type GaN would bequenched, while, the PC in p type will increase. Here, we used the UV light as thebackground light.