Sophisticated thin film growth techniques increasingly rely on the addition of a plasma component to open or widen a processing window, particularly at low temperatures. However, the addition of the plasma into the growth environment also complicates the surface dynamical evolution. Taking advantage of continued increases in accelerator-based X-ray source brilliance, this real-time study uses X-ray Photon Correlation Spectroscopy (XPCS) to elucidate the nanoscale surface dynamics during Plasma-Enhanced Atomic Layer Deposition (PE-ALD) of an epitaxial indium nitride film. XPCS examines the evolution of the coherent X-ray scattering speckle pattern, which is a fingerprint of the unique sample microstructure at each moment in time. In PE-ALD, ultrathin films are synthesized from repeated cycles of alternating self-limited surface reactions induced by temporally-separated pulses of material precursor and plasma reactant, allowing the influence of each on the evolving morphology to be examined. During the heteroepitaxial 3D growth examined here, sudden changes in surface structure during initial film growth, consistent with numerous overlapping stress-relief events, are observed. When the film becomes continuous, the nanoscale surface morphology abruptly becomes long-lived with correlation time spanning the period of the experiment. Throughout the growth experiment, there is a consistent repeating pattern of correlations associated with the cyclic growth process, which is modeled as transitions between different surface states. The plasma exposure does not simply freeze in a structure that is then built upon in subsequent cycles, but rather there is considerable surface evolution during all phases of the growth cycle.
In situ synchrotron x-ray studies were employed to develop a fundamental understanding of the low temperature atomic level processes (ALPs) for GaN substrates to develop in situ methods for preparation of epitaxy ready surfaces. An emulated gallium flash-off (GFO) ALP, followed by a hydrogen clean ALP, and a subsequent nitridation ALP are studied as a function of temperature and number of cycles. The results demonstrate that ideal GFO ALP results are achieved at a higher temperature, 500 °C, and that only ten GFO ALP cycles are needed to remove the surface oxide and result in an ordered GaN surface. Continued GFO ALP cycles at 500 °C roughen the GaN surface. GFO ALP executed at 400 °C only roughens the surface, while executing the GFO ALP at 250 °C causes uneven surface features presumably due to the incomplete removal of the oxide. The hydrogen clean ALP generally roughens the surface at all three temperatures after 30 cycles of the GFO ALP. Further, the nitridation ALP executed after 30 cycles of the GFO ALP, at any of the above temperatures, has little effect since the surface of the GaN has been roughened beyond recovery. These results provide insight into optimal GaN substrate surface preparation at temperatures consistent with the low temperature atomic layer epitaxy process.
Abstract : The Battery Charger PP-7286 ( )/U was developed to support the Laser Rangefinder MX-9838 ( )/GVS-5 which is powered by a rechargeable nickel cadmium battery, type BB-516 ( )/U and other Army equipment using generically similar batteries. The technical characteristics are described in ECOM Development Specification Number EL-CP2128-0001A. The hardware developed consisted of the Battery Charger PP-7286 ( )/U and its Transit Case CY-7670 ( )/U. The Battery Charger operates from prime power of 115 or 230 V (plus or minus 10%) 47 to 63 Hz ac. It provides five independently adjustable charging circuits, each capable of being set to charge at constant current rates from 15 through 700 milliamperes inclusive. A multiple scale meter can be switched to measure current in each of the five channels. The circuits provide constant current into any load from zero volts (short circuit) to 36 volts. A digital timer common to all circuits can be set in tenths of an hour increments from 0.1 to 19.1 hours. Time remaining in the charging cycle is displayed by an incandescent, seven segment, 3 digit display. An internal primary battery provides nonvolatile memory for the charger in the event of power interruption. A Sixth position on the meter switch allows the voltage of this battery to be measured.
Abstract : The combination of ion implantation and photolithographic patterning techniques has been applied to the fabrication of GaAs microwave FETs. This approach was adopted with the aim of providing a large number of devices having consistently predictable dc and high frequency characteristics. This memorandum concentrates on a description of the technology research carried out between 1983 and 1986 which culminated in the successful demonstration of a processing scheme meeting this objective. To validate the accuracy and repeatability of the high frequency device parameters, and X-band microwave circuit has been designed and realized. The performance of this circuit, a buffered amplifier, was very close to the design specification. The availability of a large number of reproducible, well-characterized transistors has enabled work to commence on the development of a large signal model for FETs. The preliminary work in this area is also described in this report. Great Britain. (rh)
InP MOSFET devices with a SiO2 dielectric layer have been fabricated on p-type and SI substrates. Surface mobilities in the range 250 to 750 cm2 V−1 s−1 have been routinely obtained from all substrates except those from one crystal of Fe-doped SI InP. Defect etching studies have revealed large prismatic dislocation loops in this crystal. A correlation between these observations is proposed.
In response to the interest and activity in microwave landing systems (MLSs), the capability of instrument landing systems (ILSs) is examined and a case for their continued implementation is made. The changes that have been made with respect to electronic hardware, monitoring, and antenna systems in response to more stringent demands are reviewed. It is argued that there is no technical impediment to the installation of additional and upgraded ILS installations over the 1990s and that these installations would be cost effective and pay back the investments before being displaced by MLS.< >
Valence and conduction band offsets of the InN/β-Ga2O3 type-I heterojunction have been determined to be −0.55 ± 0.11 eV and −3.35 ± 0.11 eV, respectively, using X-ray photoelectron spectroscopy. The InN layers were grown using atomic layer epitaxy on (−201) oriented commercial β-Ga2O3 substrates. Combining this data with published band offsets for the GaN and AlN heterojunctions to β-Ga2O3 has allowed us to predict the band offsets for the AlGaN, AlInN, and InGaN ternary alloys to β-Ga2O3. The conduction band offsets for InGaN and AlInN to β-Ga2O3 increased for high In concentration and, similarly, the valence band offsets for AlGaN and AlInN to β-Ga2O3 decreased at high Al concentration.
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