William R. Imler

Activation energies of Si donors in GaN

The electronic properties of Si donors in heteroepitaxial layers of GaN were investigated. The n‐type GaN layers were grown by metalorganic chemical vapor deposition and either intentionally doped with Si or unintentionally doped. The samples were evaluated by variable temperature Hall effect measurements and photoluminescence (PL) spectroscopy. For both types of samples the n‐type conductivity was found to be dominated by a donor with an activation energy between 12 and 17 meV. This donor is attributed to Si atoms substituting for Ga in the GaN lattice (SiGa). The range of activation energies is due to different levels of donor concentrations and acceptor compensation in our samples. The assignment of a PL signature to a donor–acceptor pair recombination involving the Si donor level as the initial state of the radiative transition yields the position of the optical Si donor level in the GaN bandgap at ∼Ec–(22±4) meV. A deeper donor level is also present in our GaN material with an activation energy of ∼3...

A study of parasitic reactions between NH 3 and TMGa or TMAl

The growth of AlGaN using organometallic vapor phase epitaxy has been studied as a function of reactor pressure in a horizontal reactor. At atmospheric pressure, GaN with growth efficiency comparable to that of GaAs in the same reactor is obtained. In addition, the GaN growth efficiency changes little at different reactor pressures. These results indicate that the parasitic reaction between TMGa and NH3 is not substantial in the reactor used in this study. On the other hand, A1N growth at atmospheric pressure has not been possible. By lowering the reactor pressure below 250 Torr, A1N deposition is achieved. However, the growth efficiency decreases at higher reactor pressures and higher growth temperatures, indicating that a strong parasitic reaction occurs between TMAI and NH3. For the ternary AlGaN, lower pressure also leads to more Al incorporation. The results indicate that parasitic reactions are much more severe for TMAI+NH3 than for TMGa+NH3.

High-brightness AlGaInN light-emitting diodes

Currently, commercial LEDs based on AlGaInN emit light efficiently from the ultraviolet-blue to the green portion of the visible wavelength spectrum. Data are presented on AlGaInN LEDs grown by organometallic vapor phase epitaxy (OMVPE). Designs for high-power AlGaInN LEDs are presented along with their performance in terms of output power and efficiency. Finally, present and potential applications for high-power AlGaInN LEDs, including traffic signals and contour lighting, are discussed.

High-speed photoluminescence mapping of III-V epitaxial layers for light-emitting diodes

Three examples are presented which demonstrate how photoluminescence wafer mapping is routinely used in the development and manufacturing of III-V optoelectronic materials and devices. Statistical data from the full-wafer PL scans of epitaxial layers is correlated with the device performance of fabricated light-emitting diodes, and can be used to predict the brightness, uniformity and yield of these devices.