William E. Hoke

Molecular beam epitaxial growth and device performance of metamorphic high electron mobility transistor structures fabricated on GaAs substrates

Single and double pulse doped metamorphic high electron mobility transistor (MHEMT) structures have been grown on GaAs substrates by molecular beam epitaxy. A linear indium graded buffer layer was used to expand the lattice constant. Transmission electron microscopy cross sections showed planar interfaces. Threading dislocations were not observed along both cleavage directions. For a single pulse doped MHEMT structure with an In0.56Ga0.44As channel layer, the mobilities (10 030 cm2/V s at 292 K; 32 560 cm2/V s at 77 K) and sheet density (3.2×1012 cm−2) were nearly equivalent to values obtained for the same structure grown on an InP substrate. Secondary ion mass spectroscopy measurements of a double pulse doped structure indicated no measurable migration of the silicon doping pulses. MHEMT devices with 0.15 μm gates were fabricated, tested, and compared to GaAs pseudomorphic HEMT devices of the same geometries. Above 9 GHz, the MHEMT devices exhibited lower noise figure. From 3 to 26 GHz, the associated ga...

Metalorganic growth of CdTe and HgCdTe epitaxial films at a reduced substrate temperature using diisopropyltelluride

Epitaxial films of CdTe and HgCdTe have been grown using a new metalorganic compound, diisopropyltelluride. Diisopropyltelluride is found to be less stable than the conventionally used diethyltelluride and consequently makes possible HgCdTe growth at a lower substrate temperature. Specular CdTe and HgCdTe epitaxial films have been obtained with moderate growth rates at substrate temperatures as low as 350 °C. Preliminary infrared and Hall measurements are encouraging for the application of this compound for HgCdTe growth. The reduced stability of diisopropyltelluride compared to diethyltelluride is consistent with a stability model for branched hydrocarbon molecules.

Evaluation of a new plasma source for molecular beam epitaxial growth of InN and GaN films

Abstract An RF plasma source has been integrated into a molecular beam epitaxial system for growth of nitride films. Using an optical detector on the source, the presence of nitrogen atoms in the N 2 plasma region is deduced as a function of operating conditions. The plasma source has been used to grow hexagonal wurtzite films of InN and GaN. The film-substrate interface is more abrupt for GaN than InN films. For site competition the active nitrogen species from the plasma is found to incorporate more readily than As 2 .

Low‐temperature metalorganic growth of CdTe and HgTe films using ditertiarybutyltelluride

Epitaxial films of CdTe and HgTe have been grown by metalorganic chemical vapor deposition using a new tellurium source, ditertiarybutyltelluride. This compound is demonstrated to be less stable than presently available organotellurium compounds which permits film growth at lower substrate temperatures. Specular CdTe and HgTe films have been grown at temperatures as low as 220 and 230 °C, respectively. Hall measurements performed on the HgTe films indicate good transport properties. The reduced stability of ditertiarybutyltelluride compared to other alkyl organotellurium compounds is consistent with relative stability results for branched hydrocarbon molecules.

Metalorganic vapor deposition of CdTe and HgCdTe epitaxial films on InSb and GaAs substrates

Heteroepitaxial films of CdTe and HgCdTe have been grown on InSb and GaAs substrates by metalorganic chemical vapor deposition. The CdTe growth temperature was 440 °C and the HgCdTe growth temperature was 410 °C. Specular CdTe films were obtained on (110) and (211) InSb substrates and (100) GaAs substrates. Specular surfaces of HgCdTe/CdTe/InSb and HgCdTe/CdTe/GaAs heterostructures were also obtained. X‐ray diffraction measurements indicated that the heteroepitaxial films were single crystalline. The growth plane of the CdTe films on InSb substrates was slightly misoriented from the InSb orientation. The heteroepitaxial films deposited on GaAs substrates replicated the substrate orientation.

Metalorganic growth of HgTe and CdTe at low temperatures using diallyltelluride

Both HgTe and CdTe films have been grown by metalorganic chemical vapor deposition using a novel tellurium source, diallyltelluride. This compound is found to be less stable than previously examined organotellurium compounds and permits film growth at lower substrate temperatures. This reduced stability is consistent with the presence of double bonds in diallyltelluride compared to single bonds present in alkyl tellurides. Specular HgTe films have been grown at temperatures as low as 180 °C and x‐ray analysis indicates that this material is of good crystalline quality.

High indium metamorphic HEMT on a GaAs substrate

Metamorphic growth of device structures on GaAs substrates has advanced rapidly in recent years. High quality electronic and optical devices have been demonstrated. Also long-term reliability has been achieved with low noise MHEMT devices. Most of the development emphasis has been with structures conventionally grown on InP substrates. This work is motivated by the lower cost, larger diameter, and greater robustness of GaAs substrates compared to InP substrates. However an important characteristic of metamorphic growth is the degree of freedom in choosing the In/sub x/(GaAl)/sub 1-x/As composition and consequently the lattice constant between GaAs and InAs. Consequently new device structures can be achieved which are not possible by pseudomorphic growth on either GaAs or InP substrates. In this effort, solid source MBE was used to grow metamorphic HEMT structures with high indium content. For the conventional MHEMT, the indium concentration is graded to In/sub 0.52/Al/sub 0.48/As to expand the lattice constant to that of InP. Here the indium content was graded to In/sub 0.64/Al/sub 0.36/As to achieve a larger lattice constant than InP. The resulting surface roughness was examined by AFM. For a 25 /spl mu/m x 25 /spl mu/m area, the RMS roughness was 12/spl Aring/ which is very similar to the roughness present in the conventional MHEMT with less indium content.

Properties of metamorphic materials and device structures on GaAs substrates

In this work, the structural, optical, and electrical properties of metamorphic films are examined and compared to non-metamorphic films. Results for electrical and optical devices are presented. Finally the reliability of metamorphic HEMTs is examined.

Carbon doping and lattice contraction of GaAs films grown by conventional molecular beam epitaxy

Carbon‐doped GaAs films have been grown by solid‐source molecular beam epitaxy using a graphite filament. The films were doped from 1×1015 cm−3 to 5×1019 cm−3 and the resulting mobilities are equivalent to beryllium‐doped films. A slight dependence of As4/Ga flux ratio on carbon doping was observed. The use of either As2 or As4 did not significantly affect the carbon doping concentrations. Lattice contractions were observed for films doped heavily with carbon or beryllium. For a given doping concentration the contraction is more significant for carbon doping which is consistent with the smaller tetrahedral covalent radius of carbon compared to beryllium. Good agreement between observed and calculated lattice contractions with carbon doping is obtained. Annealing studies on a film doped with carbon at 5×1019 cm−3 indicate that the electrical properties and lattice contraction are quite stable.

Metalorganic growth of high‐purity HgCdTe films

Epitaxial films of HgCdTe have been grown by metalorganic chemical vapor deposition. Diethyltelluride, dimethylcadmium, and elemental mercury were used as the starting reagents. For Hg1−xCdxTe compositions with x≤0.2, the films are n type at 300 and 77 K. From Hall measurements at 77 K a minimum carrier concentration of 1.0×1015 cm−3 and maximum mobility of 590 000 cm2/Vs were measured. Epitaxial films with x≊0.3 were also grown. The films are n type at 300 K but exhibit p‐type behavior at 77 K. p‐type carrier concentrations less than 5×1015 cm−3 were attained.