Takeshi Kikawa

40-Gb/s Direct Modulation With High Extinction Ratio Operation of 1.3-

Direct modulation at 40 Gb/s of a 1.3-mum InGaAlAs distributed feedback ridge waveguide laser is experimentally demonstrated. By combination of the high differential gain of an InGaAlAs multiquantum well active layer, a short cavity length of 100 mum, and a low-resistance notch-free grating, it achieves high bandwidth of 29 GHz and high-extinction ratio of 5 dB at 40-Gb/s modulation. Moreover, the laser operates at a record maximum ambient temperature of 60degC under 40-Gb/s directly modulation. It also achieves 40-Gb/s modulated transmission over 2 km with a low power penalty of 0.25 dB at 25degC .

\mu

We used X-ray photoelectron spectroscopy (XPS) to measure the energy discontinuity in the valence band (ΔEv) of Ga1-xNxAs/AlAs (x=0, 0.014, 0.034) and estimated ΔEv of GaNAs/GaAs by using the Al2p energy level as a reference. The change in ΔEv for GaNAs/GaAs with an increasing nitrogen content was -(0.019±0.053) eV/%N. This suggests that the valence-band edge (Ev) in GaNAs decreases in proportion to the nitrogen content. Based on the decrease in the bandgap energy of GaNAs, we found that the energy discontinuity in the conduction band (ΔEc) of GaNAs/GaAs is -(0.175±0.053) eV/%N. This large effect of bandgap bowing on the conduction band indicates that an ideal carrier confinement in the well can be obtained by using GaInNAs as an active layer in long-wavelength laser diodes.

m InGaAlAs Multiquantum Well Ridge Waveguide Distributed Feedback Lasers

Abstract Cleaning of GaAs and InP surfaces by atomic hydrogen (H∗) beam irradiation was investigated using synchrotron radiation photoemission spectroscopy and Auger electron spectroscopy. The surfaces were irradiated by a H∗ beam generated by a hot tungsten tube at a sample temperature of 360°C. After the H∗-beam irradiation, the GaAs and InP surfaces exhibited a streaky (2 × 1) and (2 × 4) RHEED pattern, respectively. It took a longer irradiation time to clean the InP surface than the GaAs surface. Photoemission spectroscopy revealed that the most persistent oxide in the H∗ cleaning process is Ga 2 O 3 for the GaAs surface, and In(PO 3 ) 3 for the InP surface.

Analysis of Band Offset in GaNAs/GaAs by X-Ray Photoelectron Spectroscopy

We have fabricated Al-free InGaAs-InGaAsP-GaAs strained quantum-well 0.98-/spl mu/m lasers with a window structure. The window structure was obtained by Si ion-implantation-induced QW intermixing. The photoluminescence and photocurrent measurements show that an implantation energy of 100 keV and a dose of 1E13 cm/sup -2/ are enough for the fabrication of the window structure in our laser structure. The threshold current of the fabricated 0.98-/spl mu/m lasers with a window structure is 20 mA and a stable lateral mode is obtained up to 300 mW, and these results suggest that there is no scattering loss or absorption due to the introduction of a window structure. The reliability of the lasers is greatly improved by the introduction of the window structure: they exhibited stable operation for more than 1000 h at 240-mW output power at 50/spl deg/C. And this results gives us an estimated lifetime of more than 200 000 h at 25/spl deg/C.

Atomic hydrogen cleaning of GaAs and InP surfaces studied by photoemission spectroscopy

The interfacial structure of nitrous-oxide- (NO-)nitrided SiO2/Si is determined on the basis of the configuration of the Pb centers and the results of physical analysis. We used electron spin-resonance analysis to observe a decrease in the number of Pb centers after NO annealing, which corresponds to the decrease in the density of interface traps. The nitrogen bonds at the interface were analyzed by x-ray photoelectron spectroscopy. An asymmetric N 1s peak at around 398 eV was detected; the peak may be decomposed into two peaks with a binding-energy difference of 0.6 eV. This core-level shift originates in the difference between the numbers of oxygen atoms that are second-nearest neighbors of the nitrogen which terminates the Pb0 and Pb1 centers.

High-power and highly reliable operation of Al-Free InGaAs-InGaAsP 0.98-/spl mu/m lasers with a window structure fabricated by Si ion implantation

Direct modulation at 12.5 Gb/s of 1.3-/spl mu/m InGaAlAs distributed feedback (DFB) ridge waveguide (RWG) lasers with low-resistance notch-free gratings running up to 115/spl deg/C is experimentally demonstrated. It was achieved by the combination of the high differential gain of an InGaAlAs MQW active layer, high characteristic temperature of RWG structure, and low-resistance notch-free grating. Moreover, successful transmission of 10-Gb/s modulated signals over 30-km standard single-mode fiber was achieved with the laser running at up to 115/spl deg/C. These results confirm the suitability of this type of laser for use as the cost-effective light source in 12.5-Gb/s and 10-Gb/s datacom applications.

An atomic model of the nitrous-oxide-nitrided SiO2/Si interface

The effect of surface Fermi level position on dc-characteristics of InP-based heterostructure bipolar transistors (HBT) is reported. The Fermi level of an InP surface covered with silicon oxide was located at an energy position close to the conduction band minimum of InP. This implies that an electron accumulation layer forms at the interface, which acts as a surface leakage path. The HBT passivated with silicon oxide films showed large excess base current and poor current gain. In contrast, the Fermi level position at the silicon nitride/InP interface was found to be near the midgap, and no electron accumulation layer was formed at the interface. The HBT passivated with silicon nitride film showed excellent dc characteristics with very small, excess base current.

12.5-gb/s direct Modulation up to 115/spl deg/C in 1.3-/spl mu/m InGaAlAs-MQW RWG DFB lasers with notch-free grating structure

Direct modulation at 12.5 Gb/s of 1.3-/spl mu/m DFB RWG lasers with low-resistance notch-free gratings running at 115/spl deg/C is experimentally demonstrated, for the first time. Moreover, 10-Gb/s modulated transmission over 30 km at 115/spl deg/C was achieved.

Passivation of InP-Based Heterostructure Bipolar Transistors in Relation to Surface Fermi Level

A Se-stabilized GaAs(001) surface is examined by extended X-ray absorption fine structure (EXAFS) analysis. The Se K-edge EXAFS shows components due not only to the first but also the second nearest neighbors, indicating that the Se atoms are incorporated into ordered atomic arrangements. Comparing the interatomic distances to those measured for Ga2Se3 and GaSe, it is concluded that the nature of the surface compound on the Se-stabilized GaAs surface is close to that of Ga2Se3.

115/spl deg/C, 12.5-Gb/s direct modulation of 1.3-/spl mu/m InGaAlAs-MQW RWG DFB laser with notch-free grating structure for datacom applications

We report the growth of BeZnCdSe quantum-well laser diode (LD) structures with a short-period superlattice cladding layer and demonstrate continuous-wave lasing in the pure-green spectral region (545 nm) at room temperature. The threshold current density and voltage of a 5-?m-wide gain-guided laser were found to be 1.7 kA/cm2 and 10.4 V, respectively. This threshold current density is sufficiently low compared with that of InGaN/GaN green LDs.