High-performance 1.55-/spl mu/m wavelength GaInAsP-InP strongly index-coupled and gain-matched distributed-feedback (DFB) lasers with periodic wirelike active regions mere fabricated by electron beam lithography, CH/sub 4//H/sub 2/-reactive ion etching, and organometallic vapor-phase epitaxial regrowth, whose index-coupling coefficient was more than 300 cm/sup -1/. In order to design lasers for low threshold current operation, threshold current dependences on the number of quantum wells and the wire width mere investigated both theoretically and experimentally. A record low threshold current density of 94 A/cm/sup 2/ among 1.55-/spl mu/m DFB lasers was successfully obtained for a stripe width of 19.5 /spl mu/m and a cavity length of 600 /spl mu/m. Moreover, a record low threshold current of 0.7 mA was also realized at room temperature under CW condition for a 2.3-/spl mu/m-wide buried heterostructure with a 200-/spl mu/m-long cavity. Finally, we confirmed stable single-mode operation due to a gain-matching effect between the standing-wave profile and the wirelike active region.

High-performance 1.55-/spl mu/m wavelength GaInAsP-InP distributed-feedback lasers with wirelike active regions

We demonstrate a short-cavity edge-emitting 0.98-/spl mu/m GaAs-based laser with semiconductor/air distributed Bragg reflector (DBR) mirrors made by reactive ion etching (RIE). The dc and small-signal modulation properties of 100-/spl mu/m-long lasers have been measured and are characterized by I/sub th/=4.5 mA and f/sub -3dB/=30 GHz under pulsed conditions, respectively. The far-field pattern of light emanating from the DBR is also measured.

Edge-emitting lasers with short-period semiconductor/air distributed Bragg reflector mirrors

The fabrication and characteristics of edge-emitting microlasers with deeply etched distributed Bragg reflector (DBR) mirrors are presented. Using reactive ion etching, the mirrors are formed at both cavity ends of a ridge waveguide laser with an GaInAs-AlGaAs single-quantum-well active layer. The devices have continuous-wave threshold currents as low as 2 and 6 mA at cavity lengths of 80 and 40 /spl mu/m, respectively. Lasing operation is achieved down to a length of 28 /spl mu/m. Diffraction limited reflectivities >75% are obtained for third-order gratings, with two DBR periods.

Edge-emitting GaInAs-AlGaAs microlasers

Short-cavity edge-emitting lasers with deeply etched distributed Bragg reflectors (DBRs) of third and second order were realised by reactive ion etching on GaInAs/AlGaAs layer structures. Diffraction limited reflectivities were achieved for third order dry etched DBR mirrors. Devices with DBRs on both cavity ends allow lasing operation for cavity lengths as short as 40 /spl mu/m.

Short-cavity edge-emitting lasers with deeply etched distributed Bragg mirrors

Fabrication techniques of high-reflectivity deeply etched semiconductor/benzocyclobutene (BCB) Bragg reflectors by multiple sequential steps of CH4/H2 reactive ion etching (RIE) and O2 plasma ashing are presented. 1.55-µm-wavelength GaInAsP/InP lasers with such reflectors exhibited low threshold current and high differential quantum efficiency with high uniformity. Threshold current as low as 7.2 mA and differential quantum efficiency as high as 50% from the front cleaved facet were obtained for a laser with a 160-µm-long active region and 15 distributed Bragg reflectors (DBRs) on the rear side. The reflectivity of the 15 DBRs was estimated to be as high as 95% from the threshold current dependence on the active region length. Finally, a preliminary aging test under room temperature CW conditions showed stable operation for more than 5000 h.

https://iopscience.iop.org/article/10.1143/JJAP.40.2269/pdf

High-Reflectivity Semiconductor/Benzocyclobutene Bragg Reflector Mirrors for GaInAsP/InP Lasers

We propose and demonstrate a new type of semiconductor laser having multiple reflector microcavities for the purpose of low threshold current operation. Very uniform multiple reflector microcavity structure was fabricated by electron beam (EB) lithography and selective wet chemical etching. Due to multiple reflection effect, threshold current density as low as 310 A/cm/sup 2/ (threshold current of 30 mA) was obtained at room temperature with the total cavity length of 64 /spl mu/m and the cavity width of 200 /spl mu/m. >

Low threshold current density operation of GaInAsP-InP laser with multiple reflector microcavities

Stripe direction dependence of mesa angle formed on (100) InP substrate was investigated by selective wet chemical etching using HCl solution with a GaInAs epitaxial mask layer. As a result, it was found that undercut-free etching can be nearly obtained with the stripe formed along the direction whereas large undercut due to anomalous etching occurred along the direction.

Stripe direction dependence of mesa angle formed on (100) InP by selective etching using HCl solution

Fundamental lasing properties of a new type of laser, which consists of a multiple micro-cavity structure with vertical grooves, was theoretically investigated based on an improved perturbation feedback theory in combination with the transfer matrix method. In order to suppress a diffraction loss between semiconductor micro-cavities, an MMC laser having grooves buried with low loss polymer (Benzocyclobutene: BCB) was proposed. Attainable maximum reflectivity was calculated to be higher than 98% for quarter wavelength wide grooves buried with BCB polymer (refractive index of 1.546, number of the micro-cavity elements of 8), which was higher than that of the semiconductor micro-cavity/air groove periodic structure. As a result, a moderately low threshold current operation (1 mA for a stripe width of 1 µm) can be obtained for the total cavity length of 45 µm with the micro-cavity length of 4.90 µm (9 elements).

Theoretical Analysis of GaInAsP/InP Multiple Micro-Cavity Laser.

The drive current of a directly modulated semiconductor laser for optical parallel data communication was investigated by taking into account both the threshold current and the differential quantum efficiency which are defined from the cavity length and the mirror reflectivities. Then the drive current required for an error free data communication (bit error rate: BER<10/sup -9/) with the bit rate of 1 Gb/s was shown as a function of the threshold current with parameters of the cavity length and the mirror reflectivities. It was found that the laser cavity design which yields the minimum drive current is almost the same condition to achieve the minimum threshold current operation when the total system loss is low (<10 dB), whereas the cavity design for higher differential quantum efficiency is required when the total system loss is much higher. When the cavity length is 100 /spl mu/m and the rear mirror reflectivity R/sub r/ is 0.99 for an example, the front mirror reflectivity R/sub f/ which gives the minimum drive current was obtained to be 0.94, 0.91, and 0.8 for the total system loss of 6, 10, and 20 dB, respectively.

Ultra-low threshold current laser for optical parallel data communication

A very uniform multiple-reflector micro-cavity structure was fabricated by electron beam (EB) lithography and selective wet chemical etching. Very small standard deviation of the gap width between micro-cavities, which was only 22 nm for the average value of 762 nm, enabled us to observe a clear modulation in PL spectrum due to multiple reflection.

N. Serizawa

Papers

Low threshold current density operation of GaInAsP-InP laser with multiple reflector microcavities

Stripe direction dependence of mesa angle formed on (100) InP by selective etching using HCl solution

Theoretical Analysis of GaInAsP/InP Multiple Micro-Cavity Laser.

Ultra-low threshold current laser for optical parallel data communication

GaInAsP/InP multiple-reflector micro-cavity structure fabricated by EB lithography and selective etching