Nitride thin films grown by pulsed laser deposition assisted by atomic nitrogen beam

Pulsed laser deposition of nitride semiconductors offers an alternative to typically employed growth techniques, such as metalorganic chemical vapor d eposition and molecular beam epitaxy. PLD can produce good quality thin fil ms at reduced growth temperatures. Growth of these materials requires provi sion of excess nitrogen in a reactive form during deposition. In our approa ch, we provide the reactive nitrogen by a low-energy atomic beam. This has the advantage of reducing dependence on substrate temperature to surmount t he kinetic barrier for compound formation while avoiding a source of hydrog en during growth. Plume wandering occurring in some cases was effectively d eterred by a dual-beam technique. Good quality films were successfully prod uced for InN, from metallic indium targets, for GaN, from both metallic gal lium and ceramic GaN targets, for ALN, from ceramic AIN targets, and for In xGa1-xN, from an In/Ga slurry. Growth rates are low except for InN, but the re is scope for increasing rates without affecting quality. Films were grow n on sapphire, silicon, and glass substrates, at a range of temperatures fr om ambient to 700 degreesC for ALN and GaN, from ambient to 400 degreesC fo r InN, and from ambient to 600 degreesC for InxGa1-xN. Films are textured i n all cases, very strongly so for the higher temperatures. Composition of t he binary materials, as determined from RES analysis, was nominally stoichi ometric. Luminescence results were obtained for all types of film, except, for lack of suitable excitation source, AlN. Direct interband luminescence was observed from thin GaN films grown directly on sapphire. Nearly all fil ms showed broad luminescence response attributed to defects, which are not yet understood. InxGa1-xN films produced had compositions from nearly pure GaN to x > 0.3, depending on growth temperature. Absorption coefficients as functions of photon energy were measured for all films on transparent subs trates. Interband edge absorption values for the binary films correspond we ll with known values. For the InxGa1-xN films the absorption edge values we re correlated to composition as determined from X-ray diffraction results. (C) 2000 Elsevier Science B.V. All rights reserved.