B. L. VanMil

High temperature limitations for GaN growth by rf-plasma assisted molecular beam epitaxy: Effects of active nitrogen species, surface polarity, hydrogen, and excess Ga-overpressure

The temperature used for growth of GaN by molecular beam epitaxy is ultimately limited by the greatly reduced growth rate related to thermal decomposition. This limiting temperature apparently varies from group to group. Factors influencing thermal decomposition are growth species (atomic versus metastable molecular nitrogen), surface polarity (N- versus Ga-polar), the presence of atomic hydrogen, and varying Ga-overpressure. Surface polarity and growth species are the predominant influence determining the onset of thermal decomposition. There are indications that the use of a significant Ga-overpressure can suppress decomposition allowing for an increase in obtainable growth temperatures for a given polarity. Electrical properties are shown to be strongly influenced by Ga-overpressure and thermal decomposition.

Photoluminescence of ZnTe and ZnTe:Cr grown by molecular-beam epitaxy

Photoluminescence (PL) from undoped and chromium-doped ZnTe epilayers was studied in the spectral range from 0.3to2.4eV over the temperature range from 5K to room temperature. Films approximately 2μm thick were grown by molecular-beam epitaxy on GaAs substrates. For undoped ZnTe, spectra are dominated by a sharp acceptor-bound-exciton line related to arsenic, with only weak emission observed due to substitutional oxygen (OTe). An analysis of strain-induced shifts in excitonic energies was performed to clarify transition assignments for two PL bands near 2.375 and 2.379eV. For ZnTe:Cr epilayers, the infrared Cr2+ emission near 2.5μm (0.5–0.6eV) was found to be a function of both doping concentration and Zn∕Te beam-equivalent-pressure ratio. Direct excitation of the Cr2+ ions with 1.89‐μm light produced emission up to room temperature. Indirect excitation with 514.5‐nm light produced emission that could be detected up to 180K. Luminescence decay curves measured from a ZnTe:Cr film ([Cr]∼1×1018cm−3) using pu...

Effect of polarity on the growth of InN films by metalorganic chemical vapor deposition

The effect of surface polarity on InN growth on GaN by metalorganic chemical vapor deposition (MOCVD) was investigated. The polarity of the InN was found to follow that of the initial GaN template as determined by a comparison of experimental and simulated convergent beam electron diffraction patterns. Under identical MOCVD growth conditions, In-polar InN was observed to nucleate and grow on Ga-polar GaN as pyramidal-shaped islands with (101¯1) as the stable surface facet. In contrast, enhanced lateral growth and reduced surface roughness were observed for N-polar InN grown on N-polar GaN. InN films grown on (0001) sapphire substrates using a thin AlN buffer under identical conditions to those used for growth on the GaN templates also exhibited reduced surface roughnesses and were determined to be N polar. A qualitative model based on the difference in surface terminations and crystal structures is proposed to explain the observed differences in the structural properties and growth modes of the In-polar a...

The effect of high energy electrons during the growth of ZnSe and ZnMgSe by molecular beam epitaxy

Electron irradiation during reflection high-energy electron diffraction is shown to affect the growth of ZnSe and ZnMgSe by molecular beam epitaxy. The high-energy electrons produce an electron stimulated desorption effect during growth of ZnSe which primarily affects adsorbed Se. Se desorption rates under electron irradiation are shown to be significantly larger than thermal desorption rates. Electron irradiation also decreases ZnSe growth rates under Zn-rich conditions. The decrease in growth rate can be suppressed by either growth under Se-rich conditions or by using high-index substrate orientations, in this case (211)B. High-energy electron irradiation does not alter composition during the growth of ZnMgSe.