Study Of Miscut Angle And P-type Contact On The Performance Stability Of GaN Based LED On Si Substrates

Gallium nitride(Ga N) has received considerable attentions for applications in light emitting diodes(LEDs) and laser diodes. But, commercial well-known substrates sapphire and Si C for Ga N are quite expensive. Instead, Si substrate is promising for its lower price and good thermal conductivity. However, the large difference between Ga N and Si substrate on their lattice parameters and thermal expansion coefficients can bring in a lager number of dislocation in the epitaxial Ga N materials, which will cause negative effects on the optical and electrical properties of LED devices. Although in recent years, the Si substrate Ga N-based LED technology has achieved a lot of achievement, but there are also a lot of work to do.In this thesis, we focus on the epitaxial growth of Ga N films on Si substrates and p-type contact on the performance stability of Ga N based LED. On the one hand, the influence of substrate miscut on properties of Ga N-based LED films grown on Si(111) was stuied,the morphology of the samples was characterized by atomic force microscopy(AFM). The Ga N crystal quality and indium contents in multiple quantum well structure(MQWs) were analyzed by high resolution X-ray diffraction(HRXRD),The optical properties of the samples were investigated by photoluminescence(PL). O n the other hand, the voltage dropping in aging progress for vertical structure chip was studied. We investigated the influence of thermal effects on the forward voltage of LED during aging process. Afterwards, the depth profiles of Mg、Ga、N、Ag and H were measured by secondary ion mass spectrometry(SIMS) in order to examine these atoms behavior in the Ag/Ga N interface and p-type Ga N. In final, the influence of N i on LED in aging process was studied by comparing the aging data of Ag and N i Ag N i Ag structures. Based on the above aspects, the following results were obtained:1. The miscut of Si(111) substrate has a significant influence for the grown-Ga N films. The optimal miscut angle of Si(111) substrate would be within 0.5°. Beyond this range, the crystal quality, surface morphology and optical propertiesof the Ga N films will deteriorate drastically.2. The paper uses wet etching method to prepare LED-samples to meet the conditions of secondary ion mass spectrometry(SIMS) test sample, and use this method in LED filed successfully.3. The generated thermal effects during the aging process will not activate the Mg acceptor and cause the forward voltage dropp ing for LED. No atoms-diffusion was observed in the Ag/Ga N interface regions. The hydrogen concentrations in the Mg-doped layer almost keep constant. We presume that during the aging progress, first, the Mg-H complex is dissociated thermally. Subsequently, the H+ may capture an injected electron, and turn into H0. On account of this conversion, hydrogen might be able to settle into a certain state where hydrogen does not passivate the Mg acceptor. By contrast, the Mg-doped layers are activated by electrical injection, which causes the increasing of p-type conductivity, and the voltage dropping of LED.4. During aging progress, the forward voltage of pure Ag structure LED dropped 0.2 V, while was very stable for N i Ag N i Ag structure, indicating the high stability of Ni-containing Si based LED devices.