R. Koda

Vertical cavity semiconductor optical amplifiers: comparison of Fabry-Perot and rate equation approaches

Accurate calculation of gain saturation properties of vertical-cavity semiconductor optical amplifiers (VCSOAs) relies on correct calculation of the average photon density in the amplifier. The most popular methods to study optical amplifiers are based on Fabry-Perot and rate equation approaches. However, they are known to give significantly different results. This paper shows that using the general Poynting theorem, it is possible to reconciliate the two methods by reconsidering the calculation of the mirror losses in the rate equation approach.

InP-based all-epitaxial 1.3-μm VCSELs with selectively etched AlInAs apertures and Sb-based DBRs

We report, for the first time, InP-based all-epitaxially grown 1.3-/spl mu/m vertical-cavity surface-emitting lasers with lattice-matched Sb-based distributed Bragg reflectors and AlInAs etched apertures. The minimum threshold current and voltage under pulsed operation were 3 mA and 2.0 V, respectively. The thermal impedance was as low as 1.2 K/mW without heat sinking. Implementation of the AlInAs etched aperture was quite effective in improving the injection efficiency and reducing the internal loss, resulting in improved differential efficiency.

Molecular-beam epitaxy growth of high-quality active regions with strained InxGa1−xAs quantum wells and lattice-matched AlxGayIn(1−x−y)As barriers using submonolayer superlattices

Submonolayer superlattices (SMS) of Ga0.47In0.53As/InAs/Ga0.47In0.52As and Ga0.47In0.53As/Al0.48In0.52As were used for the growth of strained quantum wells (QWs) and lattice-matched barriers, respectively, in the 1.55 μm active region. QWs grown with different compressive strains show excellent room-temperature photoluminescence, demonstrating the versatility of this technique. State-of-the-art current thresholds are reported for the broad-area lasers fabricated using the SMS active region.

High-differential-quantum-efficiency, long-wavelength vertical-cavity lasers using five-stage bipolar-cascade active regions

We present five-stage bipolar-cascade vertical-cavity surface-emitting lasers emitting at 1.54μm grown monolithically on an InP substrate by molecular beam epitaxy. A differential quantum efficiency of 120%, was measured with a threshold current density of 767A∕cm2 and voltage of 4.49V, only 0.5V larger than 5×0.8V, the aggregate photon energy. Diffraction loss study on deeply etched pillars indicates that diffraction loss is a major loss mechanism for such multiple-active region devices larger than 20μm. We also report a model on the relationship of diffraction loss to the number of active stages.

Al0.95Ga0.05As0.56Sb0.44 for lateral oxide-confinement layer in InP-based devices

We report a lateral oxide-confinement layer for InP-based devices using lattice-matched AlGaAsSb. The confinement-layer-induced excess loss at different widths was extracted after de-embedding the losses due to carrier diffusion, nonradiative recombination, and changes in internal injection efficiency. The results show that AlGaAsSb oxide acts as an excellent confinement layer, and shows no excess loss down to a width of 4 μm.

Rate equations of vertical-cavity semiconductor optical amplifiers

We rigorously establish the rate equations for vertical-cavity semiconductor optical amplifiers, starting from a general energy rate equation. Our results show that the conventional rate equation used so far in the literature is incorrect because of an inappropriate calculation of the mirror losses. Our calculations include the effect of amplified spontaneous emission and can be used to describe the properties of resonant-cavity-enhanced photodetectors.

Continuous-wave operation of 1.55-μm vertical-cavity surface-emitting laser with digital-alloy active region using submonolayer superlattices

For the first time, a digital-alloy active region (DAAR) consisting of submonolayer superlattices was used in a 1.55-/spl mu/m vertical-cavity surface-emitting laser. The device showed continuous-wave operation with a room-temperature threshold current (I/sub th/) of 1.2 mA, maximum output power (P/sub max/) of 0.26 mW, and a differential quantum efficiency (/spl eta//sub d/) of 21%. These results indicate that the DAAR is at least as efficient as the analog-alloy active region and provides much better control of alloy composition and strain.

InP-based 1310-1550 nm lattice-matched VCSELs

We have reviewed the recent research carried out to realize all-epitaxial VCSELs at long wavelengths. Shortcomings of the InP materials system were overcome by the use of AsSb-based alloys for DBRs and multiple active regions to combat low gain materials. The inclusion of InP spreading layers was seen to greatly improve the thermal properties of the devices. Aperturing schemes were presented which will improve these already world-class devices.

Lattice-matched Al0.95Ga0.05AsSb oxide for current confinement in InP-based long wavelength VCSELs

We examine, for the first time, Al 0.95 Ga 0.05 AsSb-oxide as the lateral current confining layer for InP-based optoelectronic devices including vertical cavity surface emitting lasers. In this paper, Al0.95Ga0.05AsSb-oxide confined broad area edge emitting lasers were used to study current confinement and optical loss. Results show that the threshold current density scales effectively down to a confining layer width of 6.5 μm and the differential efficiency remains unchanged down to 4 μm, indicating no aperture induced excess loss. This suggests that thin AlGaAsSb layers, at low oxidation temneratures. mav eet oxidized homogeneously without leaving metallic-Sb behind.

Current status of epitaxial 1.31-1.55 /spl mu/m VCSELs on InP

We have reviewed the recent research carried out to realize all-epitaxial VCSELs at long wavelengths. Shortcomings of the InP materials system were overcome by the use of AsSb-based alloys for DBRs and multiple active regions to combat low gain materials. The inclusion of InP spreading layers was seen to greatly improve the thermal properties of the devices. Two apertures were developed for the optical and current confinement. Careful placement of these apertures is expected to improve the VCSEL performance considerably.