T. Anan

Enhanced spontaneous emission from GaAS quantum wells in monolithic microcavities

Enhanced spontaneous emission has been observed with wavelength‐sized monolithic Fabry–Perot cavities containing GaAs quantum wells. With an on‐resonance cavity structure, the photoluminescence intensity increases in the cavity axis direction, and the spontaneous emission lifetime is experimentally found to decrease.

Critical layer thickness on (111)B‐oriented InGaAs/GaAs heteroepitaxy

The critical layer thickness of lattice‐mismatched InGaAs on (111)B‐oriented GaAs was investigated by monitoring surface lattice relaxation using streak spacing on the reflection high‐energy electron diffraction pattern. The critical layer thickness (hc) grown on (111)B was about twice that of a (100) under the same growth conditions. A qualitative explanation for the enhancement of hc is given based on the mechanical equilibrium theory developed by J. W. Matthews and A. E. Blakeslee [J. Cryst. Growth 27, 118 (1974)] for a strained single heterostructure.

Controlling spontaneous emission and threshold-less laser oscillation with optical microcavities

We describe the alteration of spontaneous emission of materials in optical microcavities having dimensions on the order of the emitted wavelength. Particular attention is paid to one-dimensional optical confinement structures with pairs of planar reflectors (planar microcavities). The presence of the cavity causes great modifications in the emission spectrum and spatial emission intensity distribution accompanied by changes in the spontaneous emission lifetime. Experimental results are shown for planar microcavities containing GaAs quantum wells or organic dye-embedded Langmuir-Brodgett films as light emitting layers. Also discussed are the laser oscillation properties of microcavities. A remarkable increase in the spontaneous emission coupling into the laser oscillation mode is expected in microcavity lasers. A rate equation analysis shows that increasing the coupling of spontaneous emission into the cavity mode causes the disappearance of the lasing threshold in the input-output curve. Experimentally verification is presented using planar optical microcavities confining an organic dye solution. The coupling ratio of spontaneous emission into a laser mode increases to be as large as 0.2 for a cavity having a half wavelength distance between a pair of mirrors. At this point, the threshold becomes quite fuzzy. Differences between the spontaneous emission dominant regime and the stimulated emission dominant regime are examined with emission spectra and emission lifetime analyses.

Improvement of InP/InGaAs heterointerfaces grown by gas source molecular beam epitaxy

Surface modification of a P2 beam‐exposed InGaAs surface and an As2 beam‐exposed InP surface was studied in situ using reflection high energy electron diffraction during gas source molecular beam epitaxy. It is revealed that the InP surface remained stable under As2 beam exposure after forming an InAs surface layer a few monolayers thick; the InGaAs surface became rough by P2 beam exposure. This surface roughening originates from substitutions of As to P atoms around Ga atoms. These substitutions result in the fairly reactive nature of the InGaAs surface under P2 beam exposure. From this viewpoint, we have proposed a new switching sequence which excludes surface gallium atoms by depositing one monolayer of In on the InGaAs surface before P2 beam exposure. This sequence drastically improves heterointerface quality, which was confirmed by an increase in photoluminescence intensity in InGaAs/InP short period superlattices.

Low-threshold operation of 1.3-/spl mu/m GaAsSb quantum-well lasers directly grown on GaAs substrates

GaAsSb quantum-well (QW) edge-emitting lasers grown on GaAs substrates were demonstrated. The optical quality of the QW was improved by optimizing the growth conditions and introducing a multi-QW to increase the gain. As a result, 1.27-/spl mu/m lasing of a GaAs/sub 0.66/Sb/sub 0.34/-GaAs double-QW laser was obtained with a low-threshold current density of 440 A/cm/sup 2/, which is comparable to that in conventional InP-based long-wavelength lasers. 1.30 /spl mu/m lasing with a threshold current density of 770 A/cm/sup 2/ was also obtained by increasing the antimony content to 0.36. GaAsSb QW was found to be a suitable material for use in the active layer of a 1.3-/spl mu/m vertical-cavity surface-emitting lasers.

LONG-WAVELENGTH LASING FROM INAS SELF-ASSEMBLED QUANTUM DOTS ON (311) B INP

Nanometer-scale InAs quantum dots were grown on InP by self-assembly using gas-source molecular beam epitaxy. InAs depositions of 0.33 nm in nominal thickness were found to form quantum dots on (311) B InP with a lateral dimension of about 43 nm and a density of 2×1010 cm−2. A laser structure with seven periods of the quantum dot active layers lased in a wavelength range from 1.1 to 1.4 μm at 77 K under pulsed current injection. The lasing wavelength changed to a shorter wavelength as the cavity length decreased, indicating gain saturation due to state filling effect in discrete quantum levels, which is typical in quantum dot lasers. This phenomenon can be used to achieve wide-range multiwavelength lasers for optical communication, that can be adjusted merely by changing the effective cavity length.

Spontaneous lateral alignment of In0.25Ga0.75As self-assembled quantum dots on (311)B GaAs grown by gas source molecular beam epitaxy

Spontaneous lateral alignment was observed in InGaAs quantum dots formed by self-assembly on (311)B GaAs by gas source molecular beam epitaxy. The alignment occurred in a direction inclined about 60° from the [011] direction on a (3-11) [(311)B] surface. A typical base diameter of the dots was about 120±10 nm. The heights varied from 3 to 13 nm as the nominal thickness of the InGaAs layer increased from 4 to 8 nm. The formation mechanism for the alignment is studied based on the growth thickness dependence of the dot structures. A photoluminescence linewidth of 24 meV was obtained from 9 nm high dots at 77 K, indicating the formation of a uniform dot structure.

High-speed 1.1-μm-range InGaAs VCSELs

We have developed 1.1-μm-range high-speed VCSELs based on InGaAs-QWs for high-speed and highly reliable optical interconnections. 3-dB bandwidth up to 20 GHz and error-free 30-Gbps 100 m operations were demonstrated with oxide confined VCSELs. We also developed buried tunnel junction VCSELs to further improve the relaxation oscillation frequency limit. 3-dB bandwidth up to 24 GHz and error-free 40-Gbps operations were demonstrated with these VCSELs.

Growth by molecular‐beam epitaxy and characterization of (InAs)m(GaAs)m short period superlattices on InP substrates

(InAs)m(GaAs)m short period superlattices (SPSs) have been grown by molecular‐beam epitaxy on InP substrates with their layer index m value systematically changed from 1 to 3. Their structural and electrical property dependencies on the layer index m value have been examined. During the first growth stage for the SPSs, with layer index m values of 2 and 3, two‐dimensional reflection high‐electron energy diffraction growth patterns were observed. The intended periodic structures without misfit dislocation generation were confirmed by x‐ray diffraction and transmission electron microscopy (TEM) measurements. However, the obtained electrical properties were still poor, indicating the existence of a large amount of disorder in the SPSs. On the other hand, though the thickness of consisting binary compounds was as thin as one monolayer, a high‐quality (InAs)1(GaAs)1 SPS was obtained. The highly ordered monolayer arrangement for InAs and GaAs was first observed by a TEM lattice image as well as x‐ray diffractio...

Highly Reliable High-Speed 1.1-

In this paper, we describe high-speed 1.1-μm-range oxide-confined vertical-cavity surface-emitting lasers (VCSELs) for large-scale optical interconnection applications. For achieving high data rates up to 25 Gbit/s under high temperature, we applied InGaAs/GaAsP strain-compensated multiple quantum wells (SC-MQWs) as the active layer. The developed device showed 25 Gbit/s error-free operation at 100°C. We also examined reliability of the VCSELs through accelerated life tests. The result showed an extremely long lifetime of about 10 thousand hours in MTTF under an ambient temperature of 150°C and a current density of about 19 kA/cm2. The level of reliability either equaled or surpassed that of conventional 0.85-μm VCSELs. Moreover, we revealed a typical failure mode of the device, which was caused by ≪110≫ dark line defects (DLDs) generated in the n-DBR layers under the current aperture area.