Pulsed-laser deposition produces high-quality epitaxial gallium nitride films

Pulsed-laser deposition produces high-quality epitaxial gallium nitride films

Using an excimer laser to ablate a gallium nitride (GaN) target, researchers at the University of Maryland (College Park, MD) have grown high-quality GaN films on sapphire substrates. The grou¥produced a plasma from a polycrystalline, stoichiometric GaN target by exposing it to 25-ns, 2-J/cm2 pulses from a 248-nm krypton fluoride excimer laser; the ablated material deposited and formed an epitaxial film on a sapphire substrate mounted 7 cm from the target surface. The process occurred in a stainless-steel vacuum chamber filled with ammonia (NH3) gas at pressures from 10-3 to 10-2 torr; substrate temperatures were between 800°C and 1000°C.

In tests with Rutherford backscattering spectroscopy, the 0.5- to 1.5-µm films demonstrated good crystallinity, and fits of absorption coefficient as a function of photon energy near the bandga¥revealed a bandga¥energy of 3.4 eV. Films grown at higher temperatures (950°C) showed significantly fewer defects than those grown at lower temperatures--and at increased temperatures the films showed a higher degree of stoichiometric composition, but this was accompanied by reduced growth rate. Future work will concentrate on pulsed-laser deposition fabrication of GaN and metal oxide semiconductor heterostructures.