摘要:

In situRaman spectra ofSiHx,Si–F, and Si–Si vibrations from Si surfaces in HF aqueous solutions are obtained using a highly sensitive confocal microprobe Raman system. Electrochemical roughening pretreatment and laser-assisted roughening procedure enable good quality surface Raman spectra to be obtained. The surface Raman and photoluminescence spectra from the Si surface in the etching environment and the correlation of the two types of spectra are discussed. The Raman spectroscopy is shown to have high potential in serving as an important tool forin situinvestigating of Si surface bonding during the etching process. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120877

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Raman scattering, photoluminescence (PL), and nuclear reaction analysis (NRA) have been employed to investigate the effects of rapid thermal annealing (RTA) on GaN films grown on sapphire (0001) substrates by gas-source molecular-beam epitaxy. The Raman spectra showed the presence of theE2(high) mode of GaN and shift of this mode from 572 to568 cm−1caused by annealing. The results showed that RTA has a significant effect on the strain relaxation caused by the lattice and thermal expansion misfit between the GaN epilayer and the substrate. The PL peak exhibited a blueshift in its energy position and a decrease in the full width at half maximum after annealing, indicating an improvement in the optical quality of the film. Furthermore, a green luminescence appeared after annealing and increased in intensity with increasing annealing time. This effect was attributed to H concentration variation in the GaN film, which was measured by NRA. A high H concentration exists in as-grown GaN, which can neutralize the deep level, and the H-bonded complex dissociates during RTA. This leads to the appearance of a luminescent peak in the PL spectrum. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120878

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We report a study of the ultraviolet (UV) irradiation effects on the wet chemical etching of unintentionally dopedn-type gallium nitride (GaN) layers grown on sapphire substrates. When illuminated with a 253.7 nm mercury line source, etching of GaN is found to take place in aqueous phosphorus acid(H3PO4)and potassium hydroxide (KOH) solutions ofpHvalues ranging from−1to 2 and 11 to 15, respectively. Formation of gallium oxide is observed on GaN when illuminated in diluteH3PO4and KOH solutions. These results are attributed to a two-step reaction process upon which the UV irradiation is shown to enhance the oxidative dissolution of GaN. ©1998 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.120879

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

By inserting stacked sheets of nominally 0.7 monolayer CdSe into a ZnSe matrix we create a region with strong resonant excitonic absorption. This leads to an enhancement of the refractive index on the low-energy side of the absorption peak. Efficient waveguiding can thus be achieved without increasing the average refractive index of the active layer with respect to the cladding. Processed high-resolution transmission electron microscopy images show that the CdSe insertions form Cd-rich two-dimensional (Cd, Zn)Se islands with lateral sizes of about 5 nm. The islands act as quantum dots with a three-dimensional confinement for excitons. Zero-phonon gain is observed in the spectral range of excitonic and biexcitonic waveguiding. At high excitation densities excitonic gain is suppressed due to the population of the quantum dots with biexcitons. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120880

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Optical characterization of GaN/SiC heterojunctions andp-SiC has been performed to explain the current–voltage(I–V)characteristics in GaN/SiCn-pheterojunction diodes. TheI–Vcharacteristics exhibit tunneling-assisted current with low forward “turn-on” voltages around 1.15 V as opposed to the expected drift/diffusion current with a turn on around 2.5 V. Electroluminescence (EL) measurements on these diodes revealed an infrared peak at 1.25 eV and a red peak at 1.75 eV. Photoluminescence (PL) measurements onp-SiC yielded peaks at 1.25 and 1.80 eV. Since the band gap of 6H–SiC is 3.03 eV, we attribute the EL and PL peaks to radiative transitions from the conduction band edge to a defect level and subsequently down to the valence band edge ofp-SiC. This defect level is located 1.25 eV above the valence band edge. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120881

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Highly regular arrays of steps are produced on vicinal Si(111)7×7. The step edges are atomically straight for up to2×104lattice sites. The terraces are single domain, which produces a minimum kink width of 2.3 nm (half a 7×7 unit cell) and thus a high barrier for creating kinks. Criteria for obtaining optimum step arrays are established, such as the miscut [≈1° towards (1¯1¯2)] and an annealing sequence which passes through step bunching regions quickly. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120882

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Carbon tetrachloride dissociatively adsorbs on the Ga-rich (4×2) reconstruction of GaAs (001) at 200 °C. Upon heating to 440 °C, the chlorine desorbs as GaCl, which etches the surface. Scanning tunneling micrographs reveal that this reaction transforms the (4×2) into a Ga-rich (3×2) structure that is interlaced with As-rich (2×4) phases. The (3×2) is well ordered, while the (2×4) phases exhibit a high degree of disorder. This work establishes the surface reaction pathway for carbon doping of GaAs withCCl4.©1998 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.120620

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have studied the formation of strained InAs and InP island structures on GaP surfaces grown by chemical beam epitaxy. InP grows pseudomorphically for 3 ML before island crystallization is observed by reflection high-energy electron diffraction, following a typical Stranski–Krastanov growth mode. For the growth of InAs on GaP, three-dimensional diffraction peaks are observed after 0.9 ML of InAs have been deposited, indicating a Volmer–Weber growth mode. Atomic force microscopy studies of these structures are presented and the optical properties are discussed. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120883

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We show that the addition spectra of semiconductor quantum dots in the presence of magnetic field can be studied through a theoretical scheme that allows an accurate and practical treatment of the single-particle states and electron–electron interaction up to large numbers of electrons. The calculated addition spectra exhibit the typical structures of Hund-like shell filling, and account for recent experimental findings. A full three-dimensional description of Coulomb interaction is found to be essential for predicting the conductance characteristics of few-electron semiconductor structures. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120933

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We report on the realization of etched mirror facets in GaN cavities by chemically assisted ion-beam etching. The etching conditions are adjusted to obtain a high degree of verticality and smoothness. Optical pumping experiments and gain measurements are performed in etched GaN cavities of various geometries. Stimulated emission and lasing are observed. The study of the value of the gain at threshold as a function of the cavity length allows a determination of the reflection coefficient of the etched mirror. The measured value of 15&percent; is in good agreement with the one expected for a perfect air–GaN interface. This demonstrates the high quality of the etched mirror facets. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120934

出版商:AIP    

年代:1998

数据来源: AIP