T. H. Myers

Faceted inversion domain boundary in GaN films doped with Mg

Homoepitaxial GaN films, doped with Mg, were grown by rf-plasma molecular-beam epitaxy on Ga-polarity (0001) templates. Convergent-beam electron diffraction analysis establishes that the film polarity changes from [0001] to [0001_] when the Mg flux during growth is approximately 1 ML/s. Secondary ion mass spectrometry indicates a doping concentration of ∼1020 cm−3 in the film where the inversion occurs, and a reduced Mg incorporation in the [0001_] material. Transmission electron microscopy shows that the inversion domain boundary is faceted predominantly along the {0001} and {h,h,−2h,l} planes, with l/h approximately equal to 3. Using first-principles total energy calculations, we show that the {h,h,−2h,l} segments of the boundary are stabilized by the incorporation of Mg in threefold coordinated lattice sites.

Buried p-type layers in Mg-doped InN

Variable magnetic field Hall effect, photoluminescence, and capacitance-voltage (CV) analysis have been used to study InN layers grown by plasma assisted molecular beam epitaxy. All three techniques reveal evidence of a buried p-type layer beneath a surface electron accumulation layer in heavily Mg-doped samples. Early indications suggest the Mg acceptor level in InN may lie near 110meV above the valence band maximum. The development of p-type doping techniques offers great promise for future InN based devices.

Magnesium incorporation in GaN grown by molecular-beam epitaxy

A pronounced dependence of Mg incorporation on surface polarity was observed in a series of Mg step-doped epitaxial GaN layers grown by rf-plasma-assisted molecular-beam epitaxy. Incorporation was studied for both (0001), or Ga-polarity and (0001) or N-polarity orientations. Up to a factor of 30 times more Mg was incorporated in Ga-polarity layers under certain conditions, as determined by secondary ion mass spectrometry. Measurements indicate surface accumulation of Mg occurs during growth, with stable accumulations of close to a monolayer of Mg on the Ga-polarity surface. The presence of atomic hydrogen during growth significantly increased incorporation of Mg without also incorporating potentially compensating hydrogen.

The effect of atomic hydrogen on the growth of gallium nitride by molecular beam epitaxy

GaN was grown by molecular beam epitaxy using an rf plasma source. Growth under gallium‐rich conditions at 730 °C was required to produce high quality layers as indicated by photoluminescence, Hall effect, atomic force microscopy, and x‐ray diffraction measurements. Atomic hydrogen has a significant effect for Ga‐rich growth, increasing growth rates by as much as a factor of 2.

The influence of inversion domains on surface morphology in GaN grown by molecular beam epitaxy

Growth of GaN by rf-plasma molecular beam leads to different surface morphologies for nitrogen-rich growth versus gallium-rich growth. Nitrogen-rich growth produces a significant density of pyramidal hillocks while gallium-rich growth results in flat surfaces. Differences in surface morphology were directly linked to the presence of inversion domains which originated in the nucleation layer. Nitrogen-rich growth and growth under atomic hydrogen enhanced the growth rate of inversion domains with respect to the surrounding matrix, while growth under Ga-rich conditions resulted in a more nearly equal growth rate.

Arsenic‐doped CdTe epilayers grown by photoassisted molecular beam epitaxy

We report the successful p‐type doping of CdTe films with arsenic using the photoassisted molecular beam epitaxy growth technique. These doped epilayers were grown at substrate temperatures as low as 180 °C. The room‐temperature hole concentrations in the CdTe:As layers ranged from 7×1015 to 6.2×1018 cm−3 as determined by van der Pauw–Hall effect measurements. We propose a doping mechanism responsible for the high p‐type doping levels observed in the films. The arsenic acceptor ionization energy was found to ∼58–60 meV using low‐temperature photoluminescence measurements.

The relation of active nitrogen species to high-temperature limitations for (0001̄) GaN growth by radio-frequency-plasma-assisted molecular beam epitaxy

A reduced growth rate for plasma-assisted molecular beam epitaxy of GaN often limits growth to temperatures less than 750 °C. The growth rate reduction can be significantly larger than expected based on thermal decomposition. Conditions producing a flux consisting predominantly of either atomic nitrogen or nitrogen metastables have been established using various radio-frequency sources. The use of atomic nitrogen, possibly coupled with the presence of low-energy ions, is associated with the premature decrease in growth rate. When the active nitrogen flux consists primarily of nitrogen metastables, the temperature dependence of the decrease is more consistent with decomposition rates. A significant improvement in electrical properties is observed for growth with molecular nitrogen metastables.

Controlled oxygen doping of GaN using plasma assisted molecular-beam epitaxy

High-quality (0001) and (0001)-GaN films were grown by plasma-assisted molecular-beam epitaxy to study the dependence of oxygen incorporation on polarity and oxygen partial pressure. Oxygen incorporates at a rate ten times faster on nitrogen-polar GaN than on the Ga polarity. Oxygen doping is controllable, reproducible, and produces low compensation material up to concentrations of at least 1018 cm−3 with higher levels showing significant compensation. Layers containing oxygen at levels above 1022 cm−3 exhibit severe cracking while oxygen concentrations less than 1021 cm−3 do not introduce significant strain. The oxygen incorporation rate has a weak dependence on Ga overpressure during Ga-stable growth but dramatically increases for conditions approaching N-stable growth.

Properties of HgCdTe films and Hg‐based quantum well structures grown by photoassisted molecular‐beam epitaxy

Illumination of the substrate during growth by molecular‐beam epitaxy (MBE), known as photoassisted molecular‐beam epitaxy, has been investigated for (111)B, (211)B, and (100) oriented growth of HgCdTe on CdZnTe. The results of this investigation indicate that photoassisted MBE of HgCdTe results in significant improvements in structural perfection. HgCdTe epilayers with average double‐crystal x‐ray diffraction full widths at half‐maximum of <30 arc s can be obtained for all three orientations. Dislocation line densities as low as 5×104 cm−2 have been observed. The structurally perfect HgCdTe epilayers also exhibit outstanding electrical properties after n‐type annealing. Hg‐based multilayer structures have also been grown by photoassisted MBE at North Carolina State University. HgCdTe–CdTe superlattices grown by this technique are comparable in structural quality to III–V superlattices. Hg‐based double‐heterojunction structures, suitable for fabrication of injection lasers, have also been grown. These lat...

Influence of active nitrogen species on high temperature limitations for (0001_) GaN growth by rf plasma-assisted molecular beam epitaxy

A reduced growth rate for plasma-assisted molecular beam epitaxy GaN growth often limits growth to temperatures less than 750 °C. The growth rate reduction is significantly larger than expected based on thermal decomposition. Characterization of various rf plasma source configurations indicated that a flux consisting predominantly of either atomic nitrogen or nitrogen metastables can be produced. The use of atomic nitrogen, possibly coupled with the presence of low energy ions, is associated with the premature decrease in growth rate. When the active nitrogen flux consists primarily of nitrogen metastables, the temperature dependence of the decrease is more consistent with decomposition rates. A significant improvement in electrical properties is observed for growth with molecular nitrogen metastables. In addition, atomic hydrogen stabilizes the growing surface of (0001_) GaN.