GaN and related alloys are important in that they have a large band gap which leads to applications requiring solar blindness or high temperature and powers. [1] In addition, the alloy GaInN can be made such that the entire visible spectrum is covered. This unique property leads to optoelectronic devices for printing, optical storage, lighting, and full color displays. [2,3] One of the main advantages of MBE for the growth of GaN and related alloys is that control of the active nitrogen species is growth temperature independent. This should lead to lower growth temperatures that are employed for GaN growth by metalorganic chemical vapor deposition (MOCVD) [4] and other vapor-phase techniques. This reduced growth temperature should lead to improvements in indium incorporation and p-type doping which are important for optoelectronic devices. Our focus areas in this endeavor include:

• Nucleation of AlN/GaN on sapphire as a low temperature buffer layer
• Effects of sapphire surface preparation before growth
• Effects of growth temperature
• Optimization of ammonia as a nitrogen source for both homoepitaxial and heteroepitaxial growth

This work is done in collaboration with Dr. Russell Dupuis and Dr. Ben Streetman of the Microelectronic Research Center at UT-Austin.

A new effort in nitride based semiconductors focuses on the synthesis of GaInAsN alloys. Experimental results have shown a significant bowing parameter for this semiconductor alloy such that the band gap is reduced with increasing nitrogen. [5] If indium is added, the resulting GaInAsN alloy has some important properties. For example, the band gap can be tailored to emission at 1.3 and 1.55 m m which are critical wavelengths for long haul fiber optic communications. In addition, GaInAsN can be growth pseudomorphically on GaAs which allows for the mature processing and fabrication technology of GaAs-based optoelectronics to be utilized at longer wavelengths. This opens up GaInAsN to be an important technological component for multijunction tandem solar cells. [6] Work in our lab is focused on understanding the mechanism(s) of nitrogen incorporation into GaInAs. We have recently shown that a high efficiency nitrogen RF plasma source can be used by diluting the nitrogen with argon. [7] Other main aspects being investigated are:

• Growth Temperature
• Growth Rate
• RF Plasma Conditions (power, gas mixture, etc.)
• As/N and V/III flux ratios

In addition, the structural, optical and electrical properties of GaInAsN are also being measured by a variety of techniques.