A Study To The Effects Of Growth Conditions On C, H And O Impurities In GaN-based Films On Si Substrate

As the luminous materials for new generation, GaN based LEDs have attract much attention, and its related technologies have been greatly improved in recent years. However, plenty of problems needed to be solved before GaN LEDs can be widely used in general lighting fields. Among these problems, the most urgent is to further improve light efficiency and reduce production cost. As foreign impurities, C, H and O may affect the quality of epitaxial films, properties of devices and yield of production. Hence, it is necessary to understand how to reduce the concentration of these impurities. In these paper, we have studied the influence of growth conditions on the concentration of C, H and O impurities via SIMS analysis, based on MOCVD growth of Si substrate GaN materials. Many results are listed below:1. The influences of Ⅴ/Ⅲ, growth rate and meatalorganic source on C incorporation into GaN is very significant. A high Ⅴ/Ⅲ ratio will result in a low C contamination, C concentration decrease exponentially with increasing NH3flow rate; higher growth rate cause higher C contamination, double the growth rate may raise the C concentration by6-7times; different metalorganic source may introduce different level of C contamination, growth of Al related materials has serious C contamination problem, while growth of In related martials has slightly C contamination. Compare with TMGa, TEGa may introduce less C contamination.2. Temperature, pressure and carrier gas are also affect C concentration directly, the impact of these factors is small, but very complex. Too high or too low growth temperature will cause the increase C concentration; high pressure could help to reduce C concentration, but the effect is not obvious; when NH3flow rate is large, low C contamination GaN films can be obtained by using both N2or H2as carrier gas, while for a small NH3flow rate, growth of GaN, using H2as carrier gas will lead to serious C contamination.3. H concentration in GaN films is decided by the concentration of Mg. Because Mg an H form complex during growth, H concentration is proportional to the Mg concentration in the GaN epitaxial films, the former is about1/3to1/5of the later. A subsequent annealing process can effectively remove the H content from the surface of the films. In addition, Al-based materials may lead to high H concentration. Besides these, other growth conditions do not affect the H concentration much directly.4. Because the O content is generally associated with the device sealing, the O concentration in the epitaxial layers is relatively stable and does not change much, it is usually maintained at a relatively low level which is about8～9×1016. However, using TMA1to grow Al-related materials will introduce a large number of O impurities.In this paper, we studied the influence of growth conditions of GaN on unintentionally doped impurities incorporation via secondary ion mass spectroscopy (SIMS) analysis. We correlated the impurities concentration to the growth conditions and theoretically explained how the condition affect the impurities incorporation. These work might be helpful for further improving the performance of GaN-based LEDs, and provides a experimental basis for production.