Masahisa Funemizu

High concentration Zn doping in InP grown by low‐pressure metalorganic chemical vapor deposition

High concentration Zn doping in InP grown by low‐pressure metalorganic chemical vapor deposition (MOCVD) was investigated in terms of saturated Zn and hole concentrations. A hole concentration of 4.5×1018 cm−3 was obtained using the conventional doping source (dimethylzinc). The saturated Zn and hole concentrations were almost independent of growth temperature and PH3 flow rate. However, the saturated concentrations increased with increasing growth rate. Zn in the epilayer was essentially electrically active. The Zn incorporation saturation and the accompanying rapid diffusion were thought to have originated from the increase of Zn in interstitial sites. A possibility of achieving a heavily Zn‐doped layer was demonstrated in terms of the nonequilibrium nature of the MOCVD growth.

High-speed 1.5- mu m compressively strained multi-quantum well self-aligned constricted mesa DFB lasers

A great improvement in the high-speed characteristics for compressively strained multi-quantum-well (MQW) distributed-feedback (DFB) lasers with self-aligned constricted mesa structures is described. Negative wavelength detuning is an important factor in making possible the extraction of potential advantages for the compressively strained MQW DFB lasers. A 17-GHz bandwidth, which is the highest among the 1.5- mu m MQW DFB lasers, is demonstrated. A wavelength chirp width of 0.42 nm at 10 Gb/s is obtained due to a reduced linewidth enhancement factor that has a magnitude of less than 2. Nonlinear damping K factor in a DFB laser with 45-nm negative detuning has drastically decreased to 0.13 ns, about half of that for unstrained MQW lasers. This is mainly due to an enhanced differential gain as large as 6.9*10/sup -12/ m/sup 3//s. The estimated intrinsic maximum bandwidth is 68 GHz. >

Wavelength tuning mechanism in three-electrode DFB lasers

The wavelength tuning mechanism is investigated for three-electrode distributed feedback (DFB) InGaAs-InGaAsP lasers. It is shown that the side and center sections play different roles in wavelength tuning: the former determines the effective Bragg wavelength and the latter contributes through the round-trip phase condition. The lasing wavelength is expressed in a simple form that renders the wavelength shift behavior exceedingly understandable. The indispensability of the thermal contribution to continuous broad range tuning is also clarified both theoretically and experimentally.<<ETX>>

Bias current dependence of FM efficiency in tunable three-electrode DFB lasers

The carrier-induced frequency modulation (FM) mechanism is investigated for tunable three-electrode DFB lasers. The bias current dependence of the FM efficiency in actual devices is successfully explained in a concise manner. The direction of the frequency shift (blue or red shift) depends on the position of the lasing mode in the stopband, which is determined by both the carrier and the thermal effects on the refractive index under a given bias condition.<<ETX>>

Thermal frequency drift suppression in tunable DFB lasers by plasma induced frequency shift enhancement

The authors propose enhanced-plasma-effect (EPE) lasers for coherent optical frequency division multiplexed networks. In the EPE lasers, the blue frequency shift due to the plasma effect is enhanced by incorporating a very thick p-side optical guide layer as a carrier reservoir for multiple quantum-well distributed feedback laser and it surpasses the red frequency shift due to the thermal effect. The results of demonstrating a frequency step response maintained in the blue shift region and an enhanced blue shift frequency modulation response over the whole modulation frequency range from DC are presented for the first time.<<ETX>>

Mechanism of wavelength tuning and frequency modulation in three-electrode DFB lasers

The static and dynamic characteristics of three-electrode DFB lasers are investigated. In wavelength tuning, the side sections determine the effective Bragg wavelength, while the center section acts as the active phase shifter. A continuous tuning with a wide range of 5 nm is demonstrated utilizing a requisite thermal contribution to the extension of the effective Bragg wavelength shift. The direction of the frequency shift in carrier-induced frequency modulation (FM) can be described by a single parameter-the phase shift in the center section. It is also pointed out that a wide FM bandwidth exceeding 10 GHz can be obtained for red-shifted cases, despite the modulation bandwidth of the carrier density being limited by the carrier lifetime. The interpretation presented in this paper makes the operating mechanism clearly understandable for practical use. >

Step bunching of InP caused by heavy doping of Se in metalorganic chemical vapor deposition and its application to device fabrication

We have found that step bunching occurs in heavily Se doped InP, grown by MOCVD, for both [001] and (111)B planes and that it occurs with a lower Se source gas flow rate for the (111)B plane than for the [001] plane. Using this heavy Se doping, we have successfully fabricated novel planar buried heterostructure lasers on p-InP substrates, in which the Se-doped n-InP current blocking layer does not make contact with the n-InP cladding layer.

Possibility of realizing new structures with inner fine electrodes by metalorganic chemical vapor deposition regrowth on AlSiO2 wires

We propose the possibility of realizing new structures with inner aluminum fine electrodes by metalorganic chemical vapor deposition (MOCVD) regrowth on AlSiO2 wires. AlSiO2 wires with Al electrodes insulated from the substrate by SiO2 spacers were successfully buried evenly by MOCVD regrowth, and a metal contact between Al and the epitaxial layers was formed simultaneously.