Yukie Nishikawa

Interfacial properties of single-crystalline CeO2 high-k gate dielectrics directly grown on Si (111)

Interfacial properties of single-crystalline CeO2 high-k dielectrics directly grown on Si (111) were investigated by comparing metal–insulator–semiconductor field-effect transistors (MISFETs) without any interfacial layer [(w/o-IL); direct growth of CeO2 on Si] and those with an interfacial layer (w-IL). FET characteristics, such as the drain current and the S factor, for the w/o-IL MISFET were much worse than those for the w-IL MISFET. The in-gap states attributed to the oxygen defects were detected in the CeO2 directly grown on Si by x-ray photoelectron spectroscopy measurements. The large interface state density induced by the oxygen defects at the CeO2/Si interface may deteriorate the w/o-IL MISFET performances.

Electrical Properties of Single Crystalline CeO2 High-k Gate Dielectrics Directly Grown on Si (111)

We have grown epitaxial single crystalline CeO2 directly on Si (111) by molecular beam epitaxy. Metal-insulator-semiconductor (MIS) capacitors were fabricated to evaluate electrical properties of CeO2 films. By eliminating an interfacial layer, equivalent oxide thickness (EOT) as small as 0.38 nm was obtained for a CeO2 physical thickness of 5 nm. The dielectric constant (e) was calculated to be e~52, which is two times larger than the value reported for bulk (polycrystalline) CeO2 (e~26). Enhancement of e is probably attributable to the anisotropy of the single crystalline CeO2 and/or the lattice distortion of CeO2 directly grown on Si. A leakage current density of ~ 1 A/cm2 was obtained at an equivalent electrical field of 5 MV/cm for the CeO2 MIS capacitors, which is much smaller than the expected value for SiO2 capacitors with the same EOT. It is revealed that single crystalline CeO2 is promising as an alternative gate dielectric.

Zn doping characteristics for InGaAlP grown by low‐pressure metalorganic chemical vapor deposition

Zn doping characteristics have been studied for In0.5(Ga1−xAlx)0.5P grown by low‐pressure metalorganic chemical vapor deposition, using dimethylzinc (DMZ) as a Zn dopant source. Hole concentration decreased with increasing Al composition x. For low DMZ introduction, the Zn incorporation efficiency decreased with increasing x. For high DMZ introduction, hole concentration saturation occurred as a result of the fall in Zn electrical activity and the Zn electrical activity also decreased with increasing x.

Effects of substrate misorientation on doping characteristics and band gap energy for InGaAlP crystals grown by metalorganic chemical vapor deposition

Abstract Effects of substrate misorientation on Zn and Si doping characteristics and band gap energy have been investigated for InGaAlP grown by low-pressure metalorganic chemical vapor deposition. The Zn concentration and the net acceptor concentration for In 0.5 (Ga 0.3 Al 0.7 ) 0.5 P monotonically increased with increasing tilt angle, using (100) substrates tilted towards [011], but they at fir st decreased and next increased using (100) substrates tilted towards [011]. A similar behavior was found for the tilt angle dependence of the band gap energy of undoped In 0.5 Ga 0.5 P. The Si concentration and the net donor concentration of In 0.5 (Ga 0.3 Al 0.7 ) 0.5 P gradually increased with increasing the substrate tilt angle, independent of the tilt direction. Neither the Zn nor the Si electrical activity depended on the substrate orientation.

A study of p-type doping for AlGaInP grown by low-pressure MOCVD

Abstract Doping characteristics for Mg (and Zn) in (Al x Ga 1− x ) 0.5 In 0.5 P have been studied with a view towards applying Mg (or Zn) doped AlInP to DH lasers. The solubility limits for the dopants decreased with increasing Al composition. The maximum hole concentration of Zn doped AlInP was at most 2×10 17 cm −3 , which is too low for practical use in DH lasers. The solubility limits for Mg were several times higher than those for Zn. The maximum hole concentration of Mg doped AlInP was 1×10 18 cm −3 . The Mg incorporation was considered to be limited by Mg revaporization from the growth surface. The Mg incorpolation at a constant doping-source introduction in AlGaInP increased with increasing Al composition. The proportion of electrically active Mg to total incorpolated Mg (electrical activity) does not change markedly with Al composition. The Mg electrical activity was quite low even at low doping levels.

Reduction of residual oxygen incorporation and deep levels by substrate misorientation in InGaAlP alloys

Effects of substrate misorientation on deep levels and on oxygen incorporation have been investigated in undoped In0.5(Ga1−xAlx)0.5P(x = 0.0−1.0) grown be metalorganic chemical vapor deposition (MOCVD). Deep-level transient spectroscopy (DLTS) measurements have revealed three deep levels (EDLTS = 0.42 eV, 0.64 eV and ≈ 1.0 eV). The concentrations of the deeper two deep levels increased with increasing x, and they were drastically reduced by using (100) substrate 15° off tilted towards [011]. The residual oxygen concentration was also reduced by using the off-axis substrate. It has been shown that the above-mentioned two deep levels are related to oxygen, and have deterious effects on the luminescent properties of InGaAlP alloys.

Effects of Growth Parameters on Oxygen Incorporation into InGaAlP Grown by Metalorganic Chemical Vapor Deposition

Oxygen incorporation into In0.5(Ga1-xAlx)0.5P grown by metalorganic chemical vapor deposition has been quantitatively investigated as a function of growth parameters. The oxygen concentration (NO) increased with increasing Al composition (x). Marked decreases in NO for x=0.7 and 1.0 were observed as the V/III ratio (molar flow rate ratio of group-V to group-III sources) was increased, although NO for x=0.7 was almost independent of the substrate temperature (TS). Since NO for x=1.0 was strongly affected by the amount of oxygen-containing species in trimethylaluminum (TMA), the origin of oxygen in InGaAlP is thought to be TMA. Net acceptor concentration (NA-ND) in Zn-doped InGaAlP for x=0.7 and 1.0 decreased with increasing NO. Oxygen may act as a deep donor, compensating for Zn acceptors.

High-Power InGaAlP Laser Diodes for High-Density Optical Recording

Theoretical investigation has been carried out for high-power InGaAlP visible-light laser diodes. The thin active layer, essential for preventing catastrophic optical damage of the laser facet, enhances carrier overflow and causes a deterioration in temperature characteristics. Increase in the bandgap energy difference between the active layer and the cladding layer is required in order to maintain sufficient heterobarrier height. High acceptor concentration for a p-cladding layer has a great effect on the prevention of the carrier overflow and, as a result, on the improvement of the temperature characteristics. High-power transverse-mode stabilized InGaAlP lasers, operating at high temperature, were realized by employing a composition-shifted thin active layer and a highly doped p-cladding layer. High-power operation, at over 100 mW, was achieved.

Effects of residual impurities on Zn electrical activity in Zn-doped InGaAlP grown by metalorganic chemical vapor deposition

Abstract The effects of residual impurities, such as hydrogen and oxygen, on Zn electrical activity have been studied for Zn-doped In 0.5 (Ga 1− x Al x ) 0.5 P grown by low-pressure metalorganic chemical vapor deposition. Zn electrical activity with a p-type cap l ayer grown on Zn-doped InGaAlP was found to be quite low and a high concentration of hydrogen was detected in Zn-doped InGaAlP. Zn electrical activity with an n-type cap layer was relatively high and no hydrogen was detected. The difference in Zn electrical activity with the conduction type of the cap layer may be a result of hydrogen passivation of Zn acceptors. The oxygen concentration in the InGaAlP increased abruptly for x > 0.4. The decrease in Zn electrical activity with increasing x correlated strongly with the increase in oxygen concentration with x , while Si electrical activity was unchanged with varying x . Oxygen might act as a deep donor in InGaAlP, compensating for Zn acceptors. It was thus demonstrated that Zn electrical activity in InGaAlP was significantly affected by the presence of hydrogen and oxygen.

Electrical characterization of Si-donor-related shallow and deep states in InGaAlP alloys grown by metalorganic chemical vapor deposition

Abstract Donor-related shallow and deep states in Si-doped In 0.5 (Ga 1− x Al x ) 0.5 P ( x = 0.0–1.0), grown by MOCVD, have been systematically investigated. DLTS measurements have revealed deep levels, with a constant thermal emission energy value ( E DLTS = 0.42 eV), for x 0.3. The concentration of these levels increased linearly with net donor concentration and reached a maximum at x ⋍ 0.5. It was found that these levels become the dominant donor level for conduction electrons in those alloys with x 0.3. The electron thermal activation energy, determined by Hall effect measurements, rapidly became larger with increasing Al mole fraction x above x = 0.3. This reached a maximum at x = 0.5, and decreased with increasing the mole fraction over the range 0.5≤ x ≤1.0. This dependence, of donor states on alloy composition, cannot be explained in terms of the accepted conduction band structure.