摘要:

Picosecond photoresponse of carriers in Si ion‐implanted Si samples has been measured using femtosecond transient reflectivity measurement. A threshold peak implant dose of 1016cm −2is required to achieve picosecond carrier lifetime. At this dosage, carrier lifetimes of 0.9 and 1.4 ps are measured for the as‐implanted and 400 °C annealed Si substrates, respectively. The increase in carrier lifetime upon annealing is attributed to the reduction in the concentration of trap and recombination centers. Sheet resistance also shows a strong dependence on the annealing temperature. An eightfold increase in sheet resistance is obtained for annealed samples, and a reduction in hopping conduction, manifested by thee−1/Ttemperature dependence, may be responsible for the increase in resistance. Further evidence of decreasing hopping conduction can be also observed from the more than two orders of magnitude in reduction of sheet resistance as the peak dosage decreases from 1016to 1014cm−2. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117795

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

By placing several Si &dgr;‐doped layers close to the surface of a GaAs molecular beam epitaxy–grown crystal, we achieve a compensation of the Schottky barrier and obtain a good Ohmic contact between aninsitudeposited (without breaking the vacuum) Al metallization layer and a highly modulation doped (n++) conduction layer embedded below the &dgr;‐doped layers in the GaAs crystal. When cooled to below the critical temperature (≊1.2 K) of Al, superconductivity is induced in the conductive layer of the semiconductor. We have studied the current voltage (I–V) characteristics in a planar geometry where the Al has been removed in a thin stripe. We find a manifestation of the superconducting energy gap and a rich fine structure at injection energies both below and above the gap. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117796

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We present studies of the interface abruptness of selectively oxidized AlAs/GaAs multilayer structures using transmission electron microscopy (TEM). High‐resolution cross‐sectional TEM images reveal that the interfaces between oxidized AlAs and unoxidized regions (GaAs and AlAs) are extremely abrupt on atomic scale. The widths of the transitional region are found to be within 4 monolayers for the interface between oxidized AlAs and unoxidized GaAs and 6.5 nm for the one between oxidized and unoxidized AlAs. The oxide layer thickness is found to decrease gradually from the oxidation front over a length of 200 nm. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117797

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have achieved spatially resolved photoluminescence (PL) from metalorganic vapor phase epitaxy (MOVPE) grown GaAs surfaces by near‐field scanning optical microscopy (NSOM). We have performed the topography, reflection, and PL measurements by NSOM combined with the topography measurements by atomic force microscopy (AFM) on the as‐grown and (NH4)2S‐passivated GaAs samples. The uniformity of GaAs with a thin Al0.65Ga0.35As cap layer has also been studied and compared with the (NH4) 2S treated samples. We found the submicron scale variations in PL intensity which were not correlated to the topographic features. The PL intensity variation was related to the changes in the surface state density. Semiquantitative analyses of the resolution limits of NSOM‐based PL measurements and surface state variations are presented. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117798

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have examined the kinetics of carrier relaxation in three‐dimensionally confined GaAs/AlGaAs layers obtained by growth on prepatterned GaAs(001) with time‐resolved cathodoluminescence (CL). Time‐delayed CL spectra at 87 K reveal that (i) relaxation of hot carriers into the largest 3D confined regions occurs on a time scale of a few hundred ps during the onset of luminescence, and (ii) the luminescence decay time also increases for these larger confined regions, owing to thermal reemission from QWs, diffusion across AlxGa1−xAs barriers, and carrier feeding from surrounding thinner QWs. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117799

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

In this letter we report the results of room‐temperature continuous wave and pulsed photoluminescence measurements on InGaN–GaN single heterojunctions. These InGaN–GaN heterojunctions were deposited over basal plane sapphire substrates using low pressure metalorganic chemical vapor deposition. We suggest the use of vertical cavity stimulated emission instead of spontaneous emission peak position as a good measure of the InGaN band edge. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117800

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We demonstrate the use of a scanned probe microscope (SPM) at 4 Kelvin to study electron transport through a ballistic point contact in the two‐dimensional electron gas inside a GaAs/AlGaAs heterostructure. The electron gas density profile is locally perturbed by the charged SPM tip providing information about the electron flow through the point contact. As the tip is scanned, one obtains a spatial image of the ballistic electron flux as well as the topographic profile of the structure. Calculations indicate the spatial resolution is comparable to the electron gas depth. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117801

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A technique is presented for forming a silicon‐on‐insulator material with an ultrathin buried oxide by utilizing the separation by implantation of oxygen or SIMOX method. It overcomes the problem of oxide continuity encountered during standard SIMOX processing when the O+‐implanted dose is scaled down to decrease the thickness of the buried oxide below ∼0.1 &mgr;m. To promote the formation of ultrathin buried oxides (during post‐implantation annealing), the implantation process was modified to produce a microstructure which promotes coalescence of the oxygen into a continuous layer. This was accomplished by slightly modifying the standard (≳500 °C) process so that the final increment of the dose is implanted near room temperature. This dose is chosen to selectively amorphize the region near the ion’s range which will yield a high‐defective layer during subsequent annealing. It is shown that this layer, which can consist of polysilicon, provides a template or guide upon which the oxide forms. Buried oxides prepared in this way are shown to be continuous and without Si inclusions while the standard process yields a broken layer with severe discontinuities. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117802

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have found the effects of HgTe layers on dislocations of (111)BHgCdTe layers grown on Si substrates by metalorganic vapor phase epitaxy. The dislocations in HgCdTe layers were reduced by inserting thin HgTe layers between HgCdTe and CdTe buffer layers. Using this method, the dislocation density of 2.3×106cm−2was obtained, which is less than quarter that of HgCdTe layers without HgTe. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117803

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The minority carrier lifetime has been measured onn‐type 6H‐ and 4H‐SiC epitaxial layers. We observe inherently longer lifetimes in 4H layers compared to 6H‐SiC layers. A value as high as 2.1 &mgr;s has been measured at room temperature in 4H‐SiC, however, large variations may be observed over the surface. The lifetime increases with temperature and at a typical operating temperature of a device the lifetime is close to 5 &mgr;s. The lifetime appears to be correlated with the morphology of the epitaxial film showing that the lifetime limiting defect may be related to a crystalline imperfection. A strong correlation can also be seen with the thickness of the epitaxial layers. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117804

出版商:AIP    

年代:1996

数据来源: AIP