C. Y. Hong

Diminution of the surface states on GaAs by a sulfur treatment

The surface chemical properties of a GaAs layer grown by molecular beam epitaxy were investigated by photoluminescence (PL) and photoreflectance (PR) measurements. While the intensity of the PL spectra for the sulfur‐treated GaAs, using a (NH4)2Sx solution, increased 75 times compared to that for the as‐grown GaAs, the peaks for the as‐grown GaAs measured by PR vanished after a sulfur treatment. These results indicate that the surface state acting as the nonradiative recombination centers was passivated by the sulfur. The chemical adsorption behavior resulting from the sulfur is discussed.

Deep level defects in porous silicon

This paper reports on the existence of deep level defects in the band gap of porous silicon by the photo-induced current transient spectroscopy technique combined with the results of thermovoltage and conductivity measurements. The defects are found to exhibit deep donor levels in the upper part of the band gap. It is found that the thermal emission and ionization energies of the defect increase in the range from 0.29 to 0.86 eV below the conduction band edge as the porosity increases, and it is proposed that the defects play the role of a luminescence killer.

Deep level defects of InAs quantum dots grown on GaAs by molecular beam epitaxy

The quantum dots (QDs) on S.I. GaAs were grown through the self-assembled growth by molecular beam epitaxy (MBE) and capped with GaAs of 80 nm. The densities of QDs were 3 × 10 10 6 x 10 10 cm -2 and their width about 31 34 nm. The deep level defects for samples with InAs QDs were investigated using the photoinduced current transient spectroscopy (PICTS) technique to investigate the lateral transport of the QDs sample. It was found that there are six deep levels in the range from 127 meV to 532 meV in the sample with QDs and their capture cross sections are about 1.6-7.9 × 10 -15 cm 2 . Especially, two deep levels, of which activation energies are 127 and 156 meV below the conduction band edge, might be the defect related with QDs. These defects are thought to be due to the defect related with the excess As atom or In vacancies near the QDs.

Effect of hydrogenation on defect levels in bulk n-GaAs

The hydrogenation effects on the defect levels existing in bulk n-GaAs were investigated by deep-level transient spectroscopy and photoluminescence. The three electron traps of the GaAs bulk samples were observed, and their activation energies wereEc — 0.35 eV (E1), 0.56 eV (E2), and 0.81 eV (E3). After hydrogenation at 250 °C for 3 h, the electron trap atEc — 0.35 eV was almost completely passivated and a new trap (EN1) atEc — 0.43 eV was observed. As a result of furnace annealing for 5 min at 300 °C, the EN1 trap disappeared, and the E3 trap passivated by hydrogenation reappeared. In particular, the trap E1 recovered to 90%. The photoluminescence measurements of the hydrogenated samples show that the germanium-related peak was passivated, and the intensity of the dominant bound exciton peak increased remarkably. After a thermal annealing for 15 min at 300 °C, the original intensity of the germanium-related peak was restored.

Computer simulation of Si-implanted GaAs(001) single crystals

A computer simulation based on the binary collision approximation has been performed to investigate the Si implantation efficiency, the Si depth profile, and the vacancy formation for Si‐implanted GaAs (001) crystals. The results reveal a strong dependence on the incident angle of the Si source. The calculated depth profile of Si agrees well with the experimental results from secondary‐ion mass spectroscopy. The simulated distribution of vacancies is shallower than that of Si atoms. Also, the calculated number of Ga vacancies exceeds that of As vacancies, which suggests that the Si atoms easily occupy the Ga sites and are activated as donors.

Rapid thermal annealing effects on the properties of plasma-enhanced chemical vapor deposited tungsten films

Tungsten films have been deposited onto single‐crystal silicon (Si) and silicon dioxide (SiO2) by plasma‐enhanced chemical vapor deposition with WF6‐SiH4‐H2 chemistry: the annealing effect on these films has been investigated by rapid thermal annealing. The deposition rate of the tungsten films on both sides of Si and SiO2 is linearly dependent on the SiH4/WF6 ratio up to 1 and the deposition rate is not increased beyond this ratio (SiH4/WF6=1). Phase transition from α‐W to β‐W and silicidation are observed under the annealing at 900 °C for 15 s in W films on Si. On the other hand, resistivities of W films on SiO2 are decreased under the same annealing condition. The resistivity reduction in W films on SiO2 is believed to be the results of the grain growth and point, line defect removal, and out‐diffusion of impurity atoms such as oxygen, fluorine, and silicon. In addition to this grain growth, the intensities of x‐ray diffraction peaks are increased after the rapid thermal annealing. Etching process of t...

The relation between Ga vacancy concentrations and diffusion lengths in intermixed GaAs/Al0.35Ga0.65As multiple quantum wells

Abstract Photoluminescence (PL) measurements were performed in order to investigate the intermixing behavior of GaAs/Al0.35Ga0.65 As multiple quantum wells due to thermal treatment. The PL spectra for the annealed samples show the step like signals, and show that the magnitude of the intermixing of Al and Ga induced by thermal annealing in GaAs/Al0.35Ga0.65As MQWs is different according to the depths. The results of the PL spectra obtained using a procedure of successive layer-by-layer chemical etching show that the atomic mixing is maximum near the sample surface and decreases monotonically with the depth. This result is caused by the different distribution of the diffused Ga vacancy. The potential profile of the GaAs/Al0.35Ga0.65As as a function of the diffusion length was investigated, and electron and hole energy subbands in the MQWs were calculated by a variational method making use of the calculated potential profile. The Ga vacancy concentration corresponding to the depth of the MQWs was investigated from the Al interdiffusion length and the distribution of the diffused Ga vacancy, and this result indicates that the diffusion length of Al is proportional to the logarithmic function of the Ga vacancy concentration.

Carbon impurity effects in Al‐Ga interdiffused GaAs/AlAs multiple quantum wells

Photoluminescence (PL) measurements were performed in order to investigate the carbon impurity effects on the intermixing behavior of GaAs/AlAs multiple quantum wells (MQWs) grown by molecular‐beam epitaxy. The GaAs/AlAs MQWs were annealed with a carbon source in a furnace annealing system. The PL spectra show that the magnitude of the intermixing of Al and Ga induced by thermal annealing in GaAs/AlAs MQWs increases with depth. This behavior is not in agreement with the intermixing mechanism considering vacancy injection of the surface. The nonuniformity of the intermixing as a function of the depth originated from the carbon impurities which were injected during thermal treatment.

Deep levels in Si-implanted and rapid thermal annealed semi-insulating GaAs

Deep levels have been investigated in Si-implanted and rapid-thermal-annealed semiinsulating GaAs:Cr, which was grown by a horizontal Bridgman method. Samples were implanted with a Si-dose of (1 - 5) x 1012 ions cm-2 with 100 keV energy, and treated by a two-step rapid thermal annealing process at 900 and 800° C. After these processes, three electron deep levels at 0.81, 0.53 and 0.62 eV below the conduction band and three hole deep levels at 0.89, 0.64 and 0.42 eV above the valence band were observed. The new deep levels Ec- 0.53 eV, Ec- 0.62 eV, andEv + 0.64 eV in fact, dominate the implantation and/or the thermally damaged region, but are not found in the bulk. These results indicate that high-density deep levels may be induced near or within the implanted region by rapid heating and cooling, and that these defects may effect carrier activation.

Enhancement of TiC/stainless steel interfaces by N+-implantation

Abstract TiC films were deposited on stainless-steel substrates by the reactive radio-frequency magnetron sputtering technique, and N + implantation were performed to enhance the quality of the TiC/stainless steel interface. The deposition rate of the TiC film increased linearly with increasing applied radio-frequency power, and it decreased with increasing partial-pressure ratio of the sputtering gas to the reactive gas. The stoichiometry of the TiC films and the interfacial depth profiles of the TiC/stainless steel heterostructures were investigated by Auger electron spectroscopy measurements. Removal of the oxygen at the TiC/stainless steel interface due to N + -implantation and annealing were observed. These results indicate that the N + -implanted TiC thin films grown on stainless-steel substrates can be used for advanced engineering ceramic applications.