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We present a new method in which both positive and negative pulses are used to etch silicon for fabrication of porous silicon (PS) monolayer. The optical thickness and morphology of PS monolayer fabricated with different negative pulse voltages are investigated by means of reflectance spectra, scanning electron microscopy and photoluminescence spectra. It is found that with this method the PS monolayer is thicker and more uniform. The micropores also appear to be more regular than those made by common positive pulse etching. This phenomenon is attributed to the vertical etching effect of the PS monolayer being strengthened while lateral etching process is restrained. The explanation we propose is that negative pulse can help the hydrogen cations (H+) in the electrolyte move into the micropores of PS monolayer. These H+ ions combine with the Si atoms on the wall of new-formed micropores, leading to formation of Si–H bonds. The formation of Si–H bonds results in a hole depletion layer near the micropore wall surface, which decreases hole density on the surface, preventing the micropore wall from being eroded laterally by F− anions. Therefore during the positive pulse period the etching reaction occurs exclusively only at the bottom of the micropores where lots of holes are provided by the anode.

The optical properties of porous silicon (PS) samples fabricated by pulse etching in a temperature range from −40 to 50°C have been investigated using reflectance spectroscopy, photoluminescence spectroscopy, and scanning electron microscopy (SEM). The dependence of the optical parameters, such as the refractive index n and the optical thickness (nd) of PS samples, on the etching temperature has been analyzed in detail. As the etching temperature decreases, n decreases, indicating a higher porosity, and the physical thickness of PS samples also decreases. Meanwhile, the reflectance spectra exhibit a more intense interference band and the interfaces are smoother. In addition, the intensity of the PL emission spectra is dramatically increased.

The special physicochemical environment caused by sonic_vacating provides an important outlet for the preparation of highly efficient luminescent porous silicon films.Experimental results show that sonic_chemical treatment is an effective t echnology for the improvement of the microstructure of porous silicon,and the luminescent efficiency and stability thereof.Luminescent porous silicon films,prep ared by ultrasonic-enhanced anode electrochemical etching,display better qualiti es than the samples prepared by conventionai methods widely used at present.This ultrasonic_chemical effect roots in sonic_vacating,i.e. the generation,formatio n and rapid collapse of bubbles in the etching solution.In the process of the po rous silicon being etched,the escape rate and caving_in of hydrogen bubbles in t he pores is increased as a result of the work of the ultrasonic waves,which is h elpful to the vertical etching of the pores.

Electroluminescence (EL) from Sibased organic microcavity has firstly been reported in the literature. The microcavity is made up of the central active multilayers sandwiched between a silver film and a porous silicon Bragg reflector (PSDBR), formed by electrochemical etching of p+Si substrate in the electrolyte of HF: C2H5OH:H2O. The central active multilayers consist of Al (1 nm) / LiF (05 nm) / Alq3 / Alq3: DCJTB / NPB / CuPc / ITO / SiO2． The reflectivity (relative to an Al mirror) of the PSDBR is up to 99%, and the stopband is about 160 nm wide. Resonant cavity mode appears as a tip in the reflectivity spectrum of the Sibased organic multilayer films, indicating that the Sibased organic multilayer structure is indeed a microcavity. The peak widths of the EL spetra are greatly reduced from 70 nm to 12 nm as compared with those measured from noncavity structures. Note that the EL emission from the cavity devices is singlemode, and the offresonant optical modes are highly suppressed. Moreover, an increase of a factor of about 4 of the resonant peak intensity is observed. In addition, the currentbrightnessvoltage characteristics and the effect of parameters on the lifetime of the cavity devices are also discussed. The present technique for obtaining enhanced EL emission from Sibased organic microcavity may also be another novel effective method for realizing allSibased photonic devices and optoelectronics device integration.

The construction of an organic microcavity with an organic light-emitting thin f ilm sandwiched between a porous silicon Bragg reflector and a silver film is dem onstrated.The peak widths of the PL spectra are greatly reduced from 83nm to 4nm as compared with those measured from non-cavity structures.The off-resonant opt ical modes are highly depressed.As is always observed from an optical microcavit y,the peak intensity is enhanced,and the peak position shows a blue shift with i ncreasing exit angles.

Presence of a K adlayer will promote nitridation of GaAs(100) surfaces at room temperature, as is evidenced by photoemission measurements. Following exposure of K/GaAs to pure nitrogen, there appear remarkable variations in both valence band and core level spectra, i.e., recovery of work function to a certain extent, emergence of the N2p peak in the valence band spectra and creation of chemically shifted Ga2p and As2p components in the core level spectra. For the three different K coverages we studied (1/4, 1/2 and 1ML), the 1ML one shows the strongest promotion effect.

The temperature dependence of photoluminescence (PL) in porous silicon has been investigated. It is found that the PL peak from the low porosity samples shows a red shift with decreasing temperature, but the blue shift of the PL peak is always observed in the high porosity samples. The temperature dependence of the PL peak shift observed experimentally can be qualitatively explained by the simulated curves of the luminescent efficiency versus wavelength.

Synchrotron radiation photoelectron spectroscopy (SRPES) combined with scanning electron microscopy (SEM) and gravimetric method is used to study the neutralized (NH4)2S-passivated GaAs(100) surfaces- Compared to the conventional (NH4)2S alkaline solution treatment, a thicker Ga sulfide layer and stronger Ga—S bonding on GaAs surface can be formed by dipping GaAs in neutralized (NH4)2S solution- Gravimetric data show that the etching rate of GaAs in neutralized (NH4)2S solution is about 15% lower than that in the conventional (NH4)2S solution- From SEM observation, only fewer number of etching pits with smaller size on the neutralized (NH4)2S treated GaAs surfaces can be found

A novel passivation film on GaAs surface has been grown by microwave sulfur glow discharge technique.Auger electron spectroscopy and Rutherford back scattering measurements show that the film is mainly composed of sulfur and gallium,and atomic ratio of gallium to sulfur is about 1∶1.From X-ray diffraction spectroscopy measurememt,GaS is identified to be hexagonal polycrystalline material.The refraction index and dielectric constant of GaS have also been determined.

A new method for post-treatment of PS(porous silicon), sulfur passivation by microwave plasma assistance in vacuum,is reported in this paper.Fourier transform infrared spectrum indicated that the treated sample surface is mainly covered by SiSx and SiOy.Compared with the as etched PS,the photoluminescence (PL) intensity of the sample is 3.5 times stronger,and the 4nm blueshift of the PL peak was observed experimentally;furthermore,the intensity decay of the PL peak hasnot been observed after 60d in the atmosphere.Therefore,sulfur passivation is an effective post treatment for enhancing PL intensity and stabilization of PS.

A novel passivation film on GaAs surface has been grown by microwave sulfur glow discharge technique.Electronic properties of GaS/GaAs interface have been studied by C-V,I-V, and DLTS measurements.C-V measurement shows that the properties of GaS/GaAs interface are nearly ideal and interface state density is about 1012／（cm2·eV),which agrees with result from DLTS measurement.From leak current of MIS′s structure in I-V spectra,the resistivity of GaS is estimated about 1011Ω·cm.

The ion beam producing ionization of N= has been successfully utilized as the N source for nitride growth. Cubic GaN thin films are thus grown on GaAs(100) substrates. The width of the (200) X-ray diffraction peak of the epilayer is 23′ only, and the high-resolution electron energy loss spectroscopy measurements show that the optical surface phonon of cubic GaN appears at the loss energy of 82 meV.

The room temperature deposited α-P/GaAs(100) interfaces have been studied by XPS, UPS, and LEED. The results show that P is adsorbed as clusters on the surface of GaAs at the initial stage of the interface formation, α-P film is formed as the deposition amount is further increased. The valence structures of the films so obtained are similar to those of plasma deposited α-P:H films. There are about one monolayer of P atoms bonded to Ga atoms of the substrate at the interface, α-P overlayer results in 0.2 eV lowering of GaAs surface barrier.

Temperature effects on interaction between P and GaAs (100) surface have been studied by in-situ X-ray photoemssion, uhra violet photcemission, high resolution electron energy loss specrroscopy and low energy electron diffraction techniques. The results show that annealing will make most of the amorphous P, which are deposited on GaAs(lOO) surface at room temperature, desorb with some randomly distributed P-clusters left on the surface. In these clusters, some of the P atoms are bonded to the Ga atoms of the substrate, others exist in the form of element. Higher temperature annealing will make all the left P atoms interact with the substrate and form GaAsP thin layer. Film of GaAsP solid solution will be obtained when depositing P on high temperature GaAs substrate. This film is suggested to be a promissing passi-vating film for GaAs surface.

Various reconstructions (c(2×6), (1×3) and (2×3)) of the GaSb (100) surface have been studied by LEED, XPS and UPS. All the three reconstructed surfaces are terminated by Sb atoms with some rows missing. Annealing in an Sb environment of both MBE-prepared, Sbdimerized c(2×6) reconstruction and IBA-prepared, Gaislands-existing (2×3) reconstruction leads to the same (1×3) reconstruction.

The energy dispersive relation of surface dangling bond state on InP() clean surface has been measured by the angle resolved photomission. The theoretical calculation based on a slab model and extended Huckel theory agreed well with the experimental result if a surface relaxed atomic structure model for InP() (1×1) is postulated.

The application of HREELS to the study of the Ag(100)/Na+O2 system reveals the presence of molecularly adsorbed oxygen species at room temperature. This may help explain why alkali metals can enhance the selectivity of an Ag catalyst towards the formation of C2H4O.

The ultraviolet photoelectron spectroscopy of GaAs (100) surface (4×1) structure has been measured by using a polarized UV light source. From the differential spectra between the UPS of the clean surface and the surface with adsorbed oxygen, the surface state peak located within 2eV below valence band maximum could be identified. According to the spectra obtained with s- and p-polarized light and the selection rule of electron transition, it could be shown that this surface state cosists of three peaks: the peak at 0.5eV below valence band maximum corresponding to the bridge bond states of surface Ga atoms, the peak at 0.7eV resulting from the bridge bond states of surface As atoms, and the peak at 1.3eV related to the dangling bond states.

The room temperature adsorption of water on clean and sodium predeposited InP(lll) surface has been studied by UPS and HREELS. The sticking coefficient of water on InP(lll) surface increases significantly as the surface is covered with 0.3 moiiolayer of sodium. This sticking coefficient enhancement could be shown to be related to the charge transfer between the sodium atoms and the surface phosphorous atoms. Water species adsorb On the surface mainly in the form of undissociated molecules. The existence of P-H bond related loss energy peak at 282 meV observed in HREELS suggests that a portion of water molecules may interact with sodium atoms predeposited on the surface or possibly decomposed on the surface to release free hydrogen atoms which could make bonding with surface phosphorous atoms.

The InP(l00) (4×2) reconstructed surface prepared by argon ion bombardment and post annealing under phosphorus pressure has been investigated by LEED, HREELS and UPS. It was found by HREELS that the forming of surface In-H and P-H bonds during hydrogen exposure happened almost simultaneously. By measuring the UP spectra using polarized light sources, it can be verified that the dangling bond states of surface P atoms do not possess the symmetrical characteristic with respect to the two basis vector directions of surface unit mesh. It could be deduced from the above evidences that there must exist some In vacancies on the In-rich InP (100) surface, and the dangling bonds of those P atoms which are located next to the In vacancies orientate off their normal directions. We propose here a missing row-dimer model for the atomic arrangement of InP (100) (4×2) stucture, which could explain the observed experimental qualitatively and might be used as a working model for seeking a precise surface structural model.

The interface formation process for In deposited on noncleaved GaAs (111) plane has been studied by means of photoemission speetroscopy combined with LEED pattern analysis. It is shown that the growth of three-dimensional In clusters dominates in this process. The surface Fermi level is found at 0.75±0.05 eV above VBM for all the investigated n-type samples prior to the deposition of In: these include both Ga-terminated GaAs(lll)-A and Asterminated GaAs (lll)-B faces. The Fermi level rapidly shifts to 0.90±0.05 eV above VBM during the deposition of In.