Delta-Doping And Surface Roughness Technique Of P-GaN

Gallium Nitride has been recognized as the third generation semiconductor. Not only is it used for fabrication of electronic device, but also for fabrication of optical electronic device which wavelength covers from visible light to ultraviolet. Nevertheless, the most important purpose is to fabricate illuminative LED. In conclusion, People need more cognition to GaN material and take more time to research.In my paper, it is mainly introduced that we have studied on growth and doping about GaN material via metalorgenic chemical vapor deposition in c-face Al2O3 substrate.1. The research about growth condition of unintentionally doped (UID) Gallium Nitride, mainly includes: buffer layer growth via two steps method, the influence of electrics characteristics and crystal quality with transformation on growth condition.2. The mechanism of doping GaN material and the influences of doping on the properties of GaN are studied.(1) n-type doping: Firstly, the properties of dopant and formation energy of impurity in bulk GaN are introduced. Secondly, we analyze the properties of n-typed impurity in theory, and substantiate via experimentation that high quality crystal need high pressure and temperature. Too much silicon dopant makes n-typed GaN crystal quality and morphology deteriorative, in this situation, the criterion of device manufacture can not be achieved; we have achieved such goal, which resistivity is 0.009Ωcm^-2, mobility is 240 cm²/Vs ,carrier concentration is 2.98×10¹⁸cm^-3, ionizationize efficiency is 0.903 at 1080℃and 500Torr ,We need more studies on doping utmost.(2)With the development of p-typed GaN, many kinds of optical electronic device can be in industrialization, p-typed GaN research can increase the level of device performance. In my paper, It is studied that influence on the lattice structure via magnesium doping in growth, and is explained why is so difficult to dope magnesium in bulk GaN. It is analyzed after experiment how temperature,V-III ratio and doping level affect the electronics properties and crystal quality of p-typed GaN. Actually, there is a conflict between growth temperature and doping level, because low temperature makes impurity atom more difficult get into the lattice, but active region could be destroyed in high temperature. In conclusion, at a intermediate temperature(980℃), we have prepared samples which resistivity is 2.3Ωcm^-2, carrier concentration is 3×10¹⁷cm^-3, mobility is 9cm²/Vs, XRD results are 351″and 397″in (002) and (102) face. we need a new method or process to solve the issue.(3)P-typed delta doped GaN growth: delta doping is firstly used to n-typed GaAs material growth, it can make the crystal quality more perfect than normal process. In my paper, it is explained the mechanism of delta doping, which can restrain polarity rollback and lattice distortion resulted from magnesium doping. The samples growned via delta doping technology exhibit that XRD results are 314″and 356″in (002) and (102) face, resistivity is 1.5Ωcm^-2, carrier concentration is 4.3×10¹⁸cm^-3, mobility is 9 cm²/Vs. At macroscopical morphology, exihits smooth surface in lower temperature.(4)A pre-purge step has been employed during delta-doping process, but the carrier concentration decreases by using a pre-purge step. It is found that pre-purge step result to low active surface of GaN.(5)At last, characteristics of p-InGaN has been studied, we found that hole concentration increased at condition of rich In composition and low growth temperature, but p-InGaN crystal had a poor quality at this condition, the morpholory of it can be the intuitionistic evidence.3. Surface roughness via epitaxy is a new method to enhance the extraction efficiency, has some merit such as shorter process and obvious effect, has been used to fabricate the roughness layer after p-typed GaN of LED. In the last chapter, I introduce the experiment we have done, and give some results about reflectivity curve.