摘要:

The conductivity of a hydrogenated amorphous siliconn+‐intrinsic‐n+(n‐i‐n) structure is reported as a function of temperature. The space‐charge‐limited conductivity &sgr; is shown to follow the Meyer–Neldel rule (MNR) [W. Meyer and H. Neldel, Z. Tech. Phys.18, 588 (1937)]: &sgr; =&sgr;00 exp(Ea/kT0) exp(−Ea/kT), whereEais the conductivity activation energy,kis Boltzmann’s constant, andTis the absolute temperature. The characteristic MNR parameters found are &sgr;00=10−2.4±0.1(&OHgr; cm)−1andT0=590±10 K. These values are practically equal to those previously found for the MNR in the ohmic conductivity in a series of hydrogenated amorphous siliconn‐i‐nstructures with varyingi‐layer thicknesses. It is argued that the MNR can be quantitatively explained by the statistical shift of the Fermi energy and that a single set of parameters corresponding to &sgr;00=10−3±1(&OHgr;  cm)−1andT0=550±100 K is applicable for both the space‐charge limited and the ohmic conductivity ofi‐type hydrogenated amorphous silicon. The MNR parameters are rather insensitive to density of states details.  

ISSN:0003-6951    

DOI:10.1063/1.105581

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We present an analysis of the electron wave directional coupling in two parallel asymmetric quantum well waveguides. By taking into account the effective mass difference between the wells we show that the transfer coefficient depends on the energy of the incident electron wave. A realistic configuration as an example of these kinds of electron wave couplers is examined. Its possible operation as an electron filter is suggested.

ISSN:0003-6951    

DOI:10.1063/1.105582

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The isotypep+‐Ge/p‐Al0.85Ga0.15As interface is examined in this study. It is shown that a lattice‐matched epitaxial layer ofp‐Al0.85Ga0.15onp+‐Ge acts like a minority‐carrier mirror. Evidence for this action comes from improved short‐wavelength response of ap+‐nGe solar cell and from a tenfold reduction in the dark saturation current of ap+‐nGe junction. At the same time, thep+‐Ge/p‐Al0.85Ga0.15As interface is electrically transparent to majority‐carrier hole transport. Similarity of measured specific resistivities of Ti/Au ohmic contacts directly to Ge and through ap‐Al0.85Ga0.15As layer top+Ge leads to this conclusion in spite of about 1 eV valence‐band offset at the Ge‐Al0.85Ga0.15As heterojunction interface. A possible mechanism for the hole transport through such an interface is discussed.

ISSN:0003-6951    

DOI:10.1063/1.106378

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We have studied the time constants involved in photoreflectance from several GaAs surface‐intrinsic‐n+structures. The rise and fall times were determined from digital oscilloscope traces. We find that they depend on the intensity and wavelength of the pump and probe beams. The observed photoreflectance feature does not always follow a single exponential decay. The dependence of rise and fall times on intensity and wavelength of pump and probe beams can be accounted for by a theory based on majority‐carrier flow. The characteristic time obtained can be used to determine the potential barrier height.

ISSN:0003-6951    

DOI:10.1063/1.105583

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Ga0.5In0.5P is observed to form the CuPt ordered structure during organometallic vapor phase epitaxy (OMVPE). Of the four possible {111} planes on which CuPt ordering could occur, only two are observed for growth on (001)‐oriented substrates, giving the (1¯11) and (11¯1) variants. The mechanism by which ordering occurs is not completely understood. Recent total energy calculations indicate that the phenomenon can be explained on the basis of thermodynamic considerations. Indirect evidence indicates that kinetic factors, including processes occurring at steps propagating across the surface in the two‐dimensional growth mode, affect ordering. In this letter, Ga0.5In0.5P layers have been grown on (001)GaAs substrates by OMVPE. In order to examine the effects of surface kinetic factors, the substrates were first patterned with [110] oriented grooves 5 &mgr;m wide and from 0.2 to 1 &mgr;m deep. This yields adjacent areas of epitaxial material within the grooves produced by growth via the motion of steps in opposite directions. Transmission electron diffraction reveals that the two directions of step motion produce two different variants. For exactly (001) oriented substrates, one half of the groove is filled with a single domain of the (1¯11) variant while the other half is also a single domain, but of the (11¯1) variant. For substrates misoriented by 6° to give [110] steps, the domains are asymmetric. The domains are very large, several square microns in cross section extending along the entire length of the groove. The strong intensities of the order‐induced spots indicate a high degree of order in the material grown in the grooves. These results demonstrate directly, for the first time, that kinetic factors related to the motion of steps on the surface determine the ordered structure formed. They also demonstrate the possibility of producing very large domains of ordered material.

ISSN:0003-6951    

DOI:10.1063/1.105584

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

AnnpnInP/Ga0.47In0.53As/InP heterojunction bipolar transistor with a unity‐gain frequency of 15 GHz was illuminated with ultrafast optical pulses at wavelengths of 620 and 1530 nm. The device responded to the pulses with an emitter current transient having a duration of 12 ps, corresponding to a bandwidth of ∼40 GHz. A slower photocurrent component, with a decay time of ∼100 ps, was a sensitive function of base bias and, because of the photocarrier dynamics and the grounded‐collector circuit configuration, could be nulled out.

ISSN:0003-6951    

DOI:10.1063/1.105585

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We report epitaxial growth of silicon on Si(100) at 230 °C by reactive dc magnetron sputter deposition. Growth is monitored withinsitumultiwavelength ellipsometry to determine the film microstructure. Film crystallinity depends on the partial pressure of hydrogen during deposition, and the best film is obtained with 2 mTorr H2. The films are found to have a bulk density deficit of a few percent and a low‐density layer at the film‐substrate interface. The microstructure is confirmed by transmission electron microscopy measurements. Infrared absorption and thermal hydrogen evolution measurements indicate that a large amount of molecular hydrogen is present at the substrate interface. We discuss the possible roles of hydrogen and particle bombardment in promoting epitaxial growth.

ISSN:0003-6951    

DOI:10.1063/1.105586

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We have found that, with proper pregrowth surface treatment, 6H‐SiC single‐crystal films can be grown by chemical vapor deposition (CVD) at 1450 °C on vicinal (0001) 6H‐SiC with tilt angles as small as 0.1°. Previously, tilt angles of greater than 1.5° were required to achieve 6H on 6H at this growth temperature. In addition, 3C‐SiC could be induced to grow within selected regions on the 6H substrate. The 3C regions contained few (or zero) double‐positioning boundaries and a low density of stacking faults. A new growth model is proposed to explain the control of SiC polytype in this epitaxial film growth process.

ISSN:0003-6951    

DOI:10.1063/1.105587

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We have studied reactive ion etching of Si1−xGexalloys withx≤0.15 and Ge in HBr plasmas. The etch rate of SiGe increases monotonically with the Ge content of the alloy and for a Si85Ge15alloy was &bartil;50% greater than for Si. Etch profiles are identical to those formed in singe‐crystal Si. X‐ray photoelectron spectroscopy studies shown that the surface of the etched SiGe alloys are depleted in Ge and consist of about one monolayer of brominated Si over the alloy.

ISSN:0003-6951    

DOI:10.1063/1.105588

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Epitaxial Si films have been deposited on Si(100) at 300 °C by remote plasma‐enhanced chemical vapor deposition using SiH4/H2mixtures with deposition rates as high as 25 A˚/min at these low temperatures. Hall measurements of the film show an unintentional doping level of about 1×1017cm−3with electron mobilities of 700 cm2 V−1s−1. Critical to the process is theinsitucleaning of the silicon substrate surface prior to deposition.

ISSN:0003-6951    

DOI:10.1063/1.105589

出版商:AIP    

年代:1991

数据来源: AIP