Kazuaki Nishikata

Strained GaInAs-AlGaInAs 1.5-/spl mu/m-wavelength multiquantum-well lasers loaded with GaInAs-AlInAs multiquantum barriers at the p-side optical confinement layer

Compressively strained GaInAs-AlGaInAs multiquantum-well (MQW) lasers (LDs) operating at 1.5-/spl mu/m-wavelength were fabricated with a multiquantum barrier (MQB) structure at the p-side of the optical confinement layer, using molecular beam epitaxial (MBE) growth technology. The effect of loading MQB is demonstrated from both laser performances and electro-luminescence (EL) spectra from LDs. As evidence of the suppression of carrier overflow by loading of MQB, it was confirmed from the laser performances that 1) the temperature dependence of slope efficiency was improved so that the efficiency was increased at high temperature and the maximum operating temperature was raised about 15/spl deg/C, 2) the temperature dependence of the K factor was improved, and the K factor was reduced more than 30% at high temperature. More direct evidence was observed in EL spectra from LDs. Reduction of about one magnitude was confirmed in the peak intensity of EL from the optical confinement layer. The rate of suppression of carrier overflow is discussed from above EL reduction rate. >

Structural dependence of 1.3-/spl mu/m narrow-beam lasers fabricated by selective MOCVD growth

The effect of structural parameters on the lasing characteristics of 1.3-/spl mu/m narrow beam lasers has been investigated. Monolithically integrated vertically tapered multiquantum-well (MQW) waveguide, fabricated by use of selective metal-organic chemical vapor deposition (MOCVD), is used for the expansion of the optical spot size. It is experimentally shown that the energy separation between the gain and waveguide regions that is formed simultaneously by selective MOCVD is shown to be an important parameter in order to achieve low-threshold current density and good temperature characteristics. The lengths of gain and waveguide regions have been investigated in terms of temperature characteristics of threshold current and far-field angle. A lower threshold current density and a higher characteristic temperature were obtained for longer gain region, We also have estimated the waveguide loss of the mode-field converter lasers diodes (MFC-LDs). High performance of 1.3-/spl mu/m integrated vertically tapered waveguide lasers were achieved in an optimized device.

Carrier confinement by multiple quantum barriers in 1.55 μm strained GaInAs/AlGaInAs quantum well lasers

Carrier confinement performance by multiple quantum barriers (MQB) is demonstrated in 1.55 μm strained GaInAs/AlGaInAs multiple quantum well (MQW) lasers grown by molecular beam epitaxy. The strained MQW lasers with MQB at p‐side optical confinement layer show larger characteristic temperature and slope efficiency at high temperature than those without MQB. It is also shown that the MQW lasers with MQB have less spontaneous emission from the optical confinement layer than the lasers without MQB. As another important result, it is demonstrated for the first time that the MQW lasers with MQB have less dependency of the K factor on the temperature than the lasers without MQB. These results further verify the effective carrier confinement performance of GaInAs/AlInAs MQB structure.

Attenuator integrated waveguide photodetectors (AIPD) with variable sensitivity range of 11 dB

A waveguide photodetector monolithically integrated with an optical attenuator based on the Franz-Keldysh effect at the input section is proposed. The intrinsic sensitivity of the device without attenuation is 0.25 A/W. The effective sensitivity is reduced by applying the reverse bias at the attenuator section. The largest variable sensitivity range of 11 dB is realized at the reverse bias of 32 V.

Low dark current AlGaInAsInP waveguide photodiodes using hybrid MBE and MOCVD growth

Abstract Dark current of 7pA with one cleaved facet and 20pA with an anti-reflection coating at the reverse bias voltage of 3 V was obtained for AlGaInAs InP pin waveguide photodiodes, in which an AlGaInAs absorption layer and optical confinement layers were grown by optimized molecular beam epitaxy and an upper InP cladding layer was grown by metal-organic chemical vapor deposition. This is the lowest known dark current reported for long-wavelength pin waveguide photodiodes to date.

Molecular-beam-epitaxy growth of strained Ga1−x InxAs/AlInAs/InP and application to 1.55 μm multi-quantum-well lasers

Abstract Dependence of critical layer thickness ( h c ) and photoluminescence (PL) intensity on growth temperature ( T g ) was investigated for 1% compressively strained Ga 0.32 In 0.68 As/AlInAs on InP. We found, for the first time, a strong T g dependence of h c in this system with h c of 24 nm at 500°C and 14 nm at 530°C. The PL intensity increased with T g , reaching a maximum at 530°C. We fabricated 1.55 μm multi-quantum-well (MQW) lasers with 1% compressively strained wells under optimized growth conditions. Threshold current density as low as 1.08 kA/cm 2 at a cavity length of 800 μm was obtained. This threshold current density is one of the lowest values obtained for 1.55 μm AlGaInAs MQW lasers grown by molecular beam epitaxy (MBE).

1.55 μm InGaAs/InAlAs/InP Quantum Wells with Mass-Dependent Width for Polarization-Independent Optical Modulation

We describe a new quantum well structure in 1.55 µ m materials where the effective width of the well is mass-dependent. This is advantageous for polarization-independent modulation of 1.55 µ m optical waves. An InGaAs/InAlAs multiple quantum well p-i-n diode with such a structure on an InP substrate has been fabricated for the first time, and its photocurrent spectra have been measured. We have observed a larger Stark shift for light-hole exciton than that for heavy-hole exciton, which never occurred in conventional quantum wells. Therefore, the same amount of Stark shift for both holes should be possible by adjusting such a quantum well structure with mass-dependent width.

1.5 μm wavelength compressively strained GaInAs/AlGaInAs multiquantum‐well lasers grown by molecular‐beam epitaxy with high differential gain and low threshold current density

1.5 μm GaInAs/AlGaInAs multiquantum‐well (MQW) lasers with 1% compressively strained quantum wells were grown by molecular‐beam epitaxy. The effective differential gain (g0) determined from the squared relaxation oscillation frequency versus output power relations is a high value of 9.3×10−16 cm2 in long‐wavelength lasers. On the other hand, the effective transparent carrier density (n0) of strained‐layer MQW lasers determined from the measurement of the spontaneous carrier lifetime was found to be very high, which is different from the theory of strain effects. However, by taking the carrier transport effect into account, it was shown that (1) for the strained MQW lasers the intrinsic transparent carrier density is lower than that of the lattice‐matched MQW lasers, and (2) the intrinsic value of g0 is estimated to be 28–56×10−16 cm2, which is close to the theoretically predicted value. By improving the laser structure to have better carrier transport, much higher effective differential gain and lower eff...

High Uniform Waveguide Photodiodes Fabricated on a 2-inch InP Wafer with Low Darkcurrent and High Responsivity

We have fabricated waveguide photodiodes with high uniform characteristics on a 2-inch InP wafer introducing a novel process. The 2-inch wafer fabrication procedure was carried out successfully by utilizing SiNx deposition on the back of the wafer in order to compensate wafer warp. Almost all the measured waveguide photodiodes exhibited low darkcurrent (average 419 pA, σ= 49 pA at 10 V reverse bias voltage) throughout the 2-inch wafer, and high responsivity of 0.987 A/W (σ=0.011 A/W) was obtained in a consecutive 60-channel array at the input wavelength of 1.3 µm. In addition, uniformity of frequency response was also confirmed.

GaInAsP/InP Attenuator Integrated Waveguide Photodetector (AIPD) Based on the Franz-Keldysh Effect

A waveguide photodetector monolithically integrated with an optical attenuator based on the Franz-Keldysh effect at the input section is proposed. The effective sensitivity of the device can be controlled by applying the reverse bias at the attenuator section. Using this device, the realization of a receiver module with low power consumption and small signal distortion under high input power can be expected. In our first demonstration, the intrinsic sensitivity of the device without attenuation is 0.25 A/W. The largest variable sensitivity range of 11 dB is realized at the reverse bias of 32 V.