Growth of GaInNAs by Plasma Assisted Molecular Beam Epitaxy
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The nitrogen containing alloy GaInNAs has attracted a great deal of interest recently for optoelectronic device applications at long wavelengths, especially 1.3 tm, on GaAs substrates. What has been observed is that the material quality degrades rapidly with the addition of nitrogen. In this work we systematically explore the parameter space for the growth of GainNAs using plasma-assisted MBE and inert gas dilution. Inert gas dilution allows additional control of the production of active nitrogen; thus we can independently adjust RF power, gas flow rate, and nitrogen generation, which is used to study the effects of the plasma on the growth surface. In addition to examining the effects of plasma operating conditions, we will also explore the effects of other growth parameters (arsenic to nitrogen ratio and growth temperature) on the resultant structural and optical properties. These properties will be explored by photoluminescence, SIMS, and x-ray diffraction with the goal of understanding how nitrogen incorporation affects the resultant material properties. The resulting information is used to grow high quality layers for GaNAs avalanche photodiodes with a cut-off wavelength of 1.0641tm. Introduction GaInNAs is a novel rII-V alloy that has attracted a lot of attention recently because of the possibility of growing long wavelength devices on GaAs substrates'. Because of the large negative bowing parameter, the addition of nitrogen into GaAs leads to a reduction of the bandgap and the addition of In to form the quatemary alloy GaInNAs induces a further reduction of bandgap. The larger In atom also compensates for the tensile strain caused by smaller N atom. This is useful because it allows the growth of GaInNAs that is lattice matched to GaAs2-3. In contrast to pure nitrides, which require high growth temperatures, the metastable mixed arsenide nitrides require low growth temperatures to prevent decomposition into GaAs and GaN 4. The low growth temperatures required for this alloy make it ideally suited for molecular beam epitaxy (MBE) growth. It also requires much less atomic nitrogen than that for pure nitrides, which is achieved by inert gas dilution and a highly efficient RF plasma source 5. Experiment The samples were grown in a modified Varian Gen II molecular beam epitaxy system using elemental sources for the group III elements (Ga, In and Al). The arsenic flux is provided as As 2 using a valved cracker. All samples were grown on GaAs substrates that are indium bonded to molybdenum holders. The substrate manipulator has a non-contact thermocouple design. The substrate temperatures were estimated by calibrating the thermocouple using, both an Ircon optical pyrometer and the GaAs oxide desorption temperature, and then extrapolating to the growth temperature. The active nitrogen is provided using an EPI UniBulbTM RF plasma source operating at a constant power of 300 W and a gas flow of 0.5 sccm. To control the amount of 315 Mat. Res. Soc. Symp. Proc. Vol. 618 0 2000 Materials Research Society
active nitrogen,
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