摘要:

GaAs quantum wires of a new type are fabricated on {1¯10} crystallographic facets perpendicular to the (1¯1¯1¯)Bsubstrates by selective area growth using metalorganic chemical vapor deposition. First, rectangular‐shaped AlGaAs layers are grown on a SiO2stripe‐masked GaAs (1¯1¯1¯)Bsubstrate at a high growth temperature. Next,n‐AlGaAs/GaAs modulation‐doped structures are laterally grown on {1¯10} sidewalls at a low growth temperature. The channel width of the one‐dimensional electron gas can be exactly controlled by the thickness of the first rectangular AlGaAs layer. The existence of the quasi‐one‐dimensional electron gas on {1¯10} sidewalls is confirmed by the orientation dependence of the Shubnikov‐de Hass oscillations. The advantage of this quantum wire structure is that there is no size fluctuation which is usually present when dry etching processes are used. Other applications of this selective growth on masked substrates, such as lateral superlattices, are also discussed.

ISSN:0003-6951    

DOI:10.1063/1.103487

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

50 nm period gratings were produced on thick GaAs substrates by using electron beam lithography and two‐step wet chemical etching. The size was very close to the theoretical limit of the electron beam lithography. For transferring such a fine grating onto GaAs, a two‐step wet chemical etching method was developed, where a H2SO4‐H2O2‐H2O system is first used to roughly etch the oxygen and carbon‐contaminated GaAs surface, followed by surface planarization with a Br‐CH3OH system.

ISSN:0003-6951    

DOI:10.1063/1.103488

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The ultrafast photocarrier dynamics in polysilane alloys, amorphous (SiH2)n, has been studied using the picosecond photoinduced absorption (PA) technique. For excitation below the optical gap, the PA response decays exponentially and is faster at low temperatures. This is interpreted in terms ofe‐hgeminate recombination in the small clusters (∼10 A˚) ofa‐Si:H embedded in the polysilane matrix. The PA response with above‐gap excitation is similar to that of conventionala‐Si:H; it decays much slower in the form of a power lawt−&bgr;(&bgr;<1), independent of spectral range between 1.4 and 2.2 eV. This shows that thee‐hdistance after above‐gap photogeneration is larger than the size of thea‐Si:H clusters.

ISSN:0003-6951    

DOI:10.1063/1.104228

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Magnetoresistance modulation, resulting from electron focusing, is investigated with multiparallel GaAs‐AlGaAs wires, which are defined by electron beam lithography and damageless wet‐chemical etching. Distinct focusing peaks in magnetoresistance are observed, although the samples have wires longer than a ballistic mean free path, which is derived from the focusing peak intensity. Specularity coefficientpfor the etched region boundary is also obtained asp≊1 from the focusing peak ratio. The mechanism limiting ballistic transport in the electron focusing condition is discussed, based on the temperature and the electron density dependence of the peak intensity.

ISSN:0003-6951    

DOI:10.1063/1.103489

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We have developed a new controllable method of selective and nonselective deposition of high quality aluminum by low‐pressure chemical vapor deposition using dimethylaluminum hydride with hydrogen. At first, silicon dioxide via holes on silicon substrate were selectively filled with aluminum by thermal decomposition. Then, adding the plasma excitation for 1 min, the aluminum film began to deposit nonselectively on the silicon dioxide as well as the selectively deposited aluminum. Silicon dioxide via holes were completely planarized by the selective and nonselective deposition. The single‐crystal structure of aluminum deposited selectively on silicon was observed with a new scanning microreflection high‐energy electron diffraction microscope.

ISSN:0003-6951    

DOI:10.1063/1.103490

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The tight‐binding method is applied, for the first time, to the analysis of the conduction‐band structure of GaAs‐Al0.4Ga0.6As quantum wires which are parallel to the [110] orientation. The results indicate that the effective mass of electrons parallel to the quantum wires is about 1.45 times as large as that of bulk GaAs. This increased effective mass reduces the electron mobility of the quantum wire at low temperature compared to the value which has been expected.

ISSN:0003-6951    

DOI:10.1063/1.103491

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Hydrogenated amorphous silicon thin films have been characterized using specular reflectance spectra. An ultraviolet light‐induced irreversible increase in reflectance has been attributed to changes in surface microstructure. These changes have been explained as being caused by phonons emitted during photocarrier thermalization. An irreversible increase of photoconductivity substantiates these observations.

ISSN:0003-6951    

DOI:10.1063/1.103492

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The diffusivity and solubility of Cu impurities have been measured in different structural states of amorphous Si (a‐Si) formed by MeV Si implantation. The 2.2‐&mgr;m‐thicka‐Si layers were first annealed (structurally relaxed) at 500 °C and then implanted with 200 keV Cu ions, returning a 300‐nm‐thick surface layer to the as‐implanted state. After diffusion at temperatures in the range 150–270 °C, we observe solute partitioning at a sharp phase boundary between the annealed and Cu‐implanted layers, the partition coefficient being as large as 8.2±1.3. The diffusion coefficient in annealeda‐Si is 2–5 times larger than in as‐implanteda‐Si, with activation energies of 1.39±0.15 and 1.25±0.04 eV, respectively. The data show quite strikingly the role which defects can play in thea‐Si structure.

ISSN:0003-6951    

DOI:10.1063/1.103493

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We present experimental evidence that current gain cutoff frequency (ft) values equal to or greater than those achieved with high electron mobility transistors (HEMTs) and pseudomorphic HEMTs can also be achieved by ion‐implanted GaAs and InGaAs metal‐semiconductor field‐effect transistors. These measuredftresults clearly suggest that the average electron velocity under the gate is determined primarily by the high‐field electron velocity rather than the low‐field electron mobility. Hence, we conclude that the transport properties of the two‐dimensional electron gas in HEMTs and pseudomorphic HEMTs do not make a significant contribution to the high‐frequency and high‐speed performance of these devices.

ISSN:0003-6951    

DOI:10.1063/1.103494

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We report on results of a Monte Carlo simulation that uses traveling‐wave equations for the optical field of mode‐locked diode lasers. The model includes effects of the spontaneous emission, the linewidth enhancement factor, and nonlinear gain. The results of the simulation agree with experimental observations such as the sublinear power versus current characteristics. According to this model the reduced power is a result of combined large‐signal effects. We propose to incorporate a frequency shifter into the cavity to improve the pulse energy and the use of available bandwidth.

ISSN:0003-6951    

DOI:10.1063/1.103495

出版商:AIP    

年代:1990

数据来源: AIP