摘要:

We have shown that the coherence length of electrons in a 55‐A˚‐period GaAs‐GaAlAs superlattice does not depend strongly on temperature in the range 5–292 K, varying from 17 periods at 5 K to a minimum of nine periods at room temperature. The quantum coherence was determined by photocurrent spectroscopy experiments that exploit the formation of Stark ladders in superlattices under electric fields.

ISSN:0003-6951    

DOI:10.1063/1.102882

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The carrier effective mobility &mgr;effin the inversion layer for bothn‐ andp‐channel metal‐oxide‐semiconductor field‐effect transistors with ultrathin gate dielectrics prepared by rapid thermal reoxidation (RTO) of rapid thermal nitrided (RTN) SiO2has been studied. It is found that although RTN/RTO degraded the low‐field &mgr;eff, it improved significantly the electron &mgr;effunder high normal field compared to control SiO2. The effect of RTN/RTO on the hole effective mobility has also been examined and found to be quite different than on the electron effective mobility. A physical mechanism is discussed to account for the observation.

ISSN:0003-6951    

DOI:10.1063/1.102883

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Molecular beam epitaxy (MBE) of Si on sapphire (SOS) has dramatically different and superior properties compared to chemical vapor deposited (CVD) SOS. The strain in the Si epilayer decreases by 21%. A 40% higher electron Hall mobility occurs at room temperature. At LN2temperatures the electron mobility increases to a level which is more indicative of bulk Si than of CVD SOS. The microtwin differential volume fraction profile is lower by more than an order of magnitude, and decreases below the detectable limit at 300 nm from the interface. The average Si/sapphire interface charge for MBE SOS is −8.0×1010cm−2, while the interface charge of CVD SOS is 2×1012cm−2.

ISSN:0003-6951    

DOI:10.1063/1.102884

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The transmission properties of a circular, right‐angle bend in a two‐dimensional electron waveguide are calculated. Significant reflections from such a bend would have serious consequences for the development of a quantum electron waveguide technology. The results show nearly perfect transmission around the bend, except for energies very close to the threshold for propagation in the channel. This is true even for rather sharp bends. A significant amount of mode mixing is found, however, for bends with a small radius of curvature.

ISSN:0003-6951    

DOI:10.1063/1.102885

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The oxidation of prereacted Pt films on (100) orientedn‐GaAs substrates was studied in the temperature range between 550 and 750 °C using Auger electron spectroscopy and Xe+ion profiling. The GaPt/PtAs2/GaAs structure formed during annealing in hydrogen was oxidized using a mixture of water vapor and hydrogen. The GaPt phase can be oxidized completely, whereas the inner PtAs2and GaAs interfaces are left unoxidized. The oxidation of the platinum‐gallium phase is self‐limited by the diffusion of the Ga through the gallium oxide overlayer. The oxide can be etched off to leave a structure consisting only of platinum‐arsenide on the GaAs substrate.

ISSN:0003-6951    

DOI:10.1063/1.103262

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Noncontact‐probe photocarrier lifetime measurements have been used to give rapid feedback on minority‐carrier lifetimes of epitaxial Si/SiGe layers grown by molecular beam epitaxy (MBE). In this manner, problems with impurity incorporation during the crystal growth can be rapidly diagnosed in a device‐processing‐independent fashion. These improvements in minority‐carrier lifetime translate directly into high gains in the heterojunction bipolar transistors (HJBTs). HJBT test devices fabricated from the MBE‐grown Si/SiGe layers show current gains as high as 800. The homojunction gain of this device is estimated to be ∼6, making the heterojunction gain on the order of 130.

ISSN:0003-6951    

DOI:10.1063/1.102886

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Three‐terminal real‐space transfer devices have been implemented in InGaAs/InAlAs/InGaAs heterostructure material. The use of nonalloyed contacts provides excellent ohmic contacts to the channel without compromising insulation from the second conducting layer, The observed negative differential resistance has a peak‐to‐valley ratio that typically exceeds 100, both at room temperature and cryogenic temperatures. The highest observed peak‐to‐valley ratio at 300 K was 490. With increasing heating voltage, the injection current across the InAlAs barrier rises in a sequence of sharp steps. We explain this feature by an instability caused by a positive feedback between the heating field in the channel and the local real‐space transfer current.

ISSN:0003-6951    

DOI:10.1063/1.102889

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We use reflection electron microscopy (REM) to analyze ion‐etched nanostructures defined in compound semiconductor heterostructures. This nondestructive imaging technique allows us to characterize 10‐nm‐wide features with high resolution and determine their sidewall morphology on a 1 nm scale. In addition to the inherent high‐resolution available from REM, we also obtain diffraction contrast from the heterostructure material, and we can image quantum wells. We routinely use this technique to characterize and accurately measure microfabricated structures with lateral dimensions below 20 nm.

ISSN:0003-6951    

DOI:10.1063/1.102867

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We report the first use of ellipsometry as a real‐time monitor of III‐V semiconductor crystal growth by molecular beam epitaxy, specifically growth of GaAs and AlGaAs from arsine, triethylgallium, and triethylaluminum sources. Our results provide new insight into the oxide desorption process and show a sensitivity of ±0.03 in compositionsx>0.2 for 10 A˚ thickness increments of AlxGa1−xAs during initial deposition on GaAs.

ISSN:0003-6951    

DOI:10.1063/1.102868

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Stoichiometric thin films of YBa2Cu3O7−&dgr;have been deposited on (100) silicon substrates byon‐axissingle target magnetron sputtering. The effect of oxygen resputtering was minimized through the use of much stronger than usual magnetic assemblies in the source. A magnet assembly incorporating NdB and NdFeB magnets produced a magnetic field above the target twice as large as the one produced by a standard SmCo magnet assembly. This allows for the use of lower operating voltages and a better electron racetrack confinement, resulting in little or no oxygen resputtering. We have obtained stoichiometric or near‐stoichiometric films on silicon both by dc and rf magnetron techniques at a variety of sputtering pressures and target to substrate distances.

ISSN:0003-6951    

DOI:10.1063/1.102845

出版商:AIP    

年代:1990

数据来源: AIP