摘要:

The surface morphology and crystal structure of InAlAs films grown by molecular beam epitaxy on (111)B InP substrates misoriented 1° toward [2¯11] have been investigated. Combined plane view transmission electron microscopy and atomic force microscopy observations have revealed spectacular terracelike topographies, induced by surface step bunching during the growth. Furthermore, cross section transmission electron microscopy analysis has shown the presence of threading dislocations, related to the giant steps, as well as strain inhomogeneities attributed to composition modulation. We have also demonstrated the potential use of the giant steps for local deposition of InAs. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120229

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Low temperature (250 °C) photo-oxidation of silicon initiated by aXe2*excimer lamp operating at a wavelength of 172 nm has been investigated. The induced reaction rate of 0.1 nm/min is 90 times greater than thermal oxidation at 612 °C and more than three times greater than that previously obtained at 350 °C using a low pressure mercury lamp. It was found to be strongly dependent upon oxygen pressure with the highest rates being achievable below 10 mbar. Ellipsometry, Fourier transform infrared spectroscopy, capacitance–voltage, and current–voltage measurements have been employed to characterize the oxide films and designate them as high quality. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120230

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The mean transverse energy (MTE) of electrons emitted from GaAs photocathodes was measured systematically using a new method based on adiabatic transverse expansion of an electron beam in a spatially decreasing magnetic field. Electrons with energies above the conduction band minimum are found to be thermalized with the lattice temperature of the cathode while electrons having suffered energy losses prior to their emission show enhanced transverse energies. For (Cs,O) and (Cs,F) activation layers on the same cathode the same MTE is found. By cooling the cathode with liquid nitrogen, the MTE of the high-energy electrons was reduced to≈14 meV. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120231

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Experimentally identified deep levels inp-type GaN at approximately 0.9–1, 1.4, and 1.8–2 eV above the valence-band maximum have been attributed to Ga vacancies. From the results of first-principles calculations, we find that from both energetic and electronic level structure standpoints it is necessary to consider the structural modificationVGa→Nanti+VN,resulting from the transfer of a nearest-neighbor N atom to a Ga-vacancy site(VGa)to explain the levels at 1 and 2 eV. Isolated N-antisite(Nanti)and nitrogen-vacancy(VN)defects are found to give rise to additional deep levels at 1.4 and 0.8 eV, respectively. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120232

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Stacked layers of self-assembled InP quantum dots embedded inGa0.52In0.48Phave been prepared by solid source molecular beam epitaxy. Thereby the distance between the dot layers has been varied from 2 to 16 nm. Cross sectional transmission electron microscopy shows that the InP dots are aligned in the growth direction [100]. As the distance between the dot layers is reduced, each dot of the first dot layer is reproduced in the upper layers, and this leads to an improvement of the dot size homogeneity of the stacked InP dot system. This is confirmed by photoluminescence (PL) measurements, which demonstrate a very narrow linewidth of 26 meV for a triple layer with 2 nm separation between the dot layers in comparison with a linewidth of 41 meV for a single layer sample. At the same time, the PL peak of the dots is shifted by 72 meV to lower energies which is ascribed to a reduced strain and strong electrical coupling between the densely stacked InP dots. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120233

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report direct excitation of optically active Er centers in porous Si. Excitation spectroscopy performed close to the intracenter4I15/2→4I11/2and4I15/2→4I9/2transitions ofEr3+(4f11)ions allows us to identify two kinds of Er centers in porous Si: (i) Er diffused into porous nanograins with lower than cubic symmetry and (ii) Er centers incorporated in an amorphous silicalike matrix. The latter show much weaker thermal quenching of theEr3+emission which decreases only by a factor of eight when the temperature is increased from 4.2 K up to 360 K. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120234

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In this letter, we report on the reaction between Si andN2in the temperature range of 760–1050 °C, in a rapid thermal processing chamber. Gas phase impurities such asH2O,O2,andH2,which can outgas from the cold walls of the chamber, mediate theSi/N2reaction, resulting in the formation ofSiOxNy.The oxynitridation can be explained by equilibrium chemical thermodynamics, in contrast to the case of oxynitridation usingN2Oor NO, where the nitrogen is incorporated under nonequilibrium conditions. Using nuclear reaction analysis, we have measured nitrogen contents as high as2.5×1015 N/cm2(the equivalent of more than 3 monolayers) in these new dielectrics. They can be reoxidized to form ultrathin (2 to 3 nm) dielectrics. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120235

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The growth kinetics of Si dots grown on 6H-SiC(0001) by molecular beam epitaxy were studied in real time by reflection high-energy electron diffraction. The critical thickness for the Stranski–Krastanov growth mode transition was found to be kinetically delayed leading to a gradual decrease of this thickness with increasing temperature(T).AtT<625 °Cand coverages below the critical thickness, a post-deposition evolution of dots is clearly established. The dot growth process is, under these conditions, mainly determined by the mass transfer out of the two-dimensional layer towards the Si dots. The dots grown on top of a 1 monolayer (ML) thick wetting layer are quantum sized with typical dimensions of 5–6 nm in height and 20–30 nm in diameter after a long post-deposition evolution times at 2–3 ML coverages. Above 625 °C and coverages above the critical thickness, the dot growth is only determined by surface-diffusion kinetics resulting in the growth of larger dots. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120236

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The choice of germanium as a substrate for CdTe and HgCdTe (MCT) epitaxial films is discussed. Ge appears to be a good candidate to solve the weakness of CdTe homosubstrates. Direct growth of CdTe(331) B 4° off epitaxial films was achieved on a Ge (001) substrate tilted 8° around [11¯0] by molecular beam epitaxy (MBE). Hence MCT(331) 4° off MBE epilayers were grown and characterized. The surface morphology was smooth and mirrorlike. X-ray double-crystal rocking curve on (331) planes showed full-width at half-maximum of 130 arc sec. Transmission electron microscopy is also reported to show the misfit accommodation at the CdTe/Ge interface; two domains were observed close to the interface but only a (331) orientation remained after a 50-nm-thick growth. The first photodiodes on MCT on Ge were fabricated and exhibited high performances: for a cutoff wavelength value of 5.24 &mgr;m atT=77 K,the shunt impedance measured was6.6×109 &OHgr;and theR0Aproduct was1.8×105 &OHgr; cm2.©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120237

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We present a simple and novel method of resistlessly patterning GaAs substrates with an oxide mask. The GaAs surface native oxide is optically modified into a stable gallium oxide mask, which then allows InAs to be grown with excellent selectivity by chemical beam epitaxy. The conventional approach to pattern wafers for selective growth is to use photoresist to pattern the silicon nitride or oxide first deposited on the wafers. Photoresist residue can remain even after elaborate cleaning and the molecular scale features can impede selectivity during growth. This method is a one-step resistless process that eliminates such photoresist related problems. Our understanding of the patterning process and results on the selective growth of InAs are presented. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120238

出版商:AIP    

年代:1997

数据来源: AIP