The Controllable Preparation And Luminescent Properties Of Silicon-based GaN

Gallium nitride (GaN) with wide-bandgap was widely used in optoelectronicdevices, for instance, light emitting diodes (LEDs), lasers diodes (LDs), solar cells，due to its excellent photoelectric properties. In our previous studies, GaN/Si-NPAnanoheterostructure array was prepared by chemical vapor deposition (CVD)technique using the substrate of Si-NPA. Yellow and NIR light emission wererealized in electroluminescence. In this paper, we studied the influence of time ofdepositing platinum, growing temperature, pressure of ammonia and annealing onmorphology, structure, reflectance spectrum and volt-ampere characteristics,photoluminescence, electroluminescence of GaN/Si-NPA. The main results of thispaper are as follows:1. Preparation, morphology and structure of GaN/Si-NPAIn this paper, the GaN/Si-NPA nanoheterostructures were synthesized onSi-NPA adopting platinum catalysts through the method of CVD. The samples keptthe array structure of Si-NPA after depositing GaN. The morphologies of GaNnanostructures changed from nanograins to a mixture of nanograins and nanowires asthe depositing-platinum time increasing. There was the same trend when enhancingthe growing temperature or pressure of ammonia. XRD patternes showed that thestructures of GaN nanostuctures were wurtzite. According to Scherrer equation, thenanograins size became larger with the prolonging of depositing-platinum time, so asto increasing growing temperature or ammonia pressure. The amorphologies of GaNnanograins could not be changed by annealing at800℃for1hour, but the nanograinsize increased slightly.2. The reflectance property of GaN/Si-NPAThe reflectivity of the GaN/Si-NPA increased gradually with prolonging ofdepositing-platinum time. As growing temperature or ammonia pressure increasing,the reflectivity of the samples also increased. There was a clear absorption edge in allsamples. When the GaN nanograin size was smaller, relative big number of photons were absorbed by GaN and substrate or transmitted finally, relative small number ofphotons were reflected by the GaN nanograins, and thus the reflectivity of the samplewas lower. When the GaN nanograin size was bigger, the reflectivity was higher. Thereason was relative large amount of photons were reflected by the GaN film, andrelatively few photons were absorbed by GaN and substrate or transmitted. Therefore,the reflectivity of the sample was higher. Prolonging of depositing-platinum time,increasing growing temperature or increasing the pressure of ammonia could makenanograin size bigger, so the reflectivity increased accordingly.3. The photoluminescence properties of GaN/Si-NPA nanoheterostructureThere were two luminous peaks in the photoluminescence spectrum, the peakpositions were at~370nm,~550nm respectively. The peak at~370nm was theintrinsic peak of GaN, and the peak at~550nm was yellow luminous peak, whichwas due to the defect levels inside the nanograins. The two peaks became strongerwhen the time of depositing platinum extended, attributing to the crystal quantity ofGaN on substrate increased, when the depositing time prolonged. Similarly, the twopeak strength increased with growth temperature or ammonina pressure increased,and the cause analysis was the same as before. The intrinsic peak of the sample withdepositing platinum5s exhibited a blue-shift with respect to the sample sprayed25s,45s. This phenomenon showed that the blue shift of the intrinsic peak position couldbe correlated with the quantum confinement effect of GaN nanograins。4. The volt-ampere characteristic and carrier transport mechanism of GaN/Si-NPAThe volt-ampere characteristic of GaN/Si-NPA was tested at the roomtemperature, and the test results showed that all the samples had rectification property.With the prolonging of depositing platinum time, the leakage current of samplesdecreased, which also indicated that the defect levels decreased and the quality of theinterface of samples improved. The samples showed the same trend when the growthtemperature increased or the ammonina pressure increased. After annealed, theleakage current of samples decreased obviously, which illustrated that the defectlevels could decrease by annealing. Fitting on the volt-ampere characteristic curves,we found that there were two ways of carrier transport mechanisms in theGaN/Si-NPA nanoheterojunction. One was ohms transmission in low voltage, and another was the space charge limited current transmission in high voltage.Thetransition process of the two kinds of transfer mode meaned that the defect energylevels in the heterojunction were filled.5. The electroluminescent characteristics of GaN/Si-NPAResearch showed that there was a broad yellow luminous peak at~530nm underthe lower forward voltage of all samples. The intensity of the peak increased with thethickness of the GaN film. Therefore, the intensity of the peak increased when thetime of depositing platinum prolonged, the pressure of the ammonia increased, or thegrowth temperature increased. The yellow peak had a red-shift with the growthtemperature increased, which was due to the presence of different contents of Gavacancies in GaN nanograins. With the increase of the voltage, another NIR lightluminous peak occurred at~815nm except the luminous peak at~530nm. Alongwith the increase of the applied voltage the strength of the yellow luminous peakincreased first and then decreased to a constant walue, while the intensity of the NIRlight peak continued to increase. The analysis indicated that the yellow luminous peakwas originated from the radiative recombination luminescence of defect energy levelsinside GaN nanograins, while the NIR luminous peak was derived from the radiativerecombination between electrons from the bottom of conduction band of GaN andholes from the top of valance band of Si-NPA.