The longer-wavelength quantum well in an AlGaAs/GaAs asymmetric dual quantum well laser structure was selectively removed by localized intermixing. High Si-doping on each side of the longer-wavelength well caused intermixing during an anneal under a SiN_x cap, while leaving the other nearby well intact. During an anneal under an exposed GaAs surface layer, both quantum wells remained intact. By patterning the surface with alternating SiN_x and exposed GaAs, the longer-wavelength quantum well was selectively intermixed under the SiN_x. Integrated broad area lasers were fabricated with threshold current density and external quantum efficiency of 260 A/cm² and 30%/facet at a wavelength of 751 nm in capped regions and 195 A/cm², 32%/facet at 824 nm in the uncapped regions. This technique can be used to fabricate close spacing multi-wavelength laser arrays.

Etch-stop layers have proven essential in fabricating devices such as distributed Bragg reflector (DBR) laser arrays which require a high degree of uniformity and precise depth positioning of the gratings. In this report, we investigate the dependence of the threshold current density and external quantum efficiency on the p-dopants' starting position in InGaAs/GaAs/AlGaAs quantum well graded-index separate-confinement heterostructure (GRINSCH) lasers with a GaAs etch-stop layer. The laser structures were grown by molecular-beam epitaxy with As₂. With the etch-stop layer approximately 200 nm above the active region's top AlGaAs graded layer, it is found that a significant fraction of injected carriers will recombine in the etch-stop layer if this layer is not sufficiently doped and if the p- dopants are not near enough to the graded layer in the active region. This results in a very high threshold current, a very low efficiency, and the presence of a high-energy peak, corresponding to the GaAs etch-stop layer acting as a quantum well, in the electroluminescence (EL) spectrum. On the other hand, with the dopants positioned correctly, we obtain very low threshold current densities and see no evidence of EL emission from the etch-stop layer. The experimental results are consistent with computer modeling performed with a commercial simulator. Results will also be presented on multiple-wavelength DBR lasers made from these structures.

This manuscript reviews our efforts in demonstrating state-of-the-art planar, batch-fabricable, high-performance vertical-cavity surface-emitting lasers (VCSELs). All performance requirements for short-haul data communication applications are clearly established. We concentrate on the flexibility of the established proton-implanted AlGaAs-based (emitting near 850 nm) technology platform, focusing on a standard device design. This structure is shown to meet or exceed performance and producibility requirements. These include > 99% device yield across 3-in-dia. metal-organic vapor phase epitaxy (MOVPE)-grown wafers and wavelength operation across a > 100-nm range. Recent progress in device performance [low threshold voltage (V_th equals 1.53 V); threshold current (I_th equals 0.68 mA); continuous wave (CW) power (P_cw equals 59 mW); maximum and minimum CW lasing temperature (T equals 200 degree(s)C, 10 K); and wall-plug efficiencies ((eta) _wp equals 28%)] should enable great advances in VCSEL-based technologies. We also discuss the viability of VCSELs in cryogenic and avionic/military environments. Also reviewed is a novel technique, modifying this established platform, to engineer low-threshold, high-speed, single- mode VCSELs.

Optimized molecular-beam epitaxial growth of pseudomorphic MQWs, the application of abrupt and spatially-localized carbon doping, and the development of short-cavity coplanar ridge-waveguide structures with high-quality chemically-assisted ion-beam etched facets have been combined to fabricate GaAs-based MQW lasers which have achieved damping-limited direct modulation bandwidths exceeding 40 GHz. More detailed measurements indicate intrinsic modulation bandwidths exceeding 60 GHz for devices with p-doped active regions. The reduced linewidth enhancement factor, (alpha) , observed in these lasers also indicates their suitability for low-chirp high-speed direct modulation. The laser design has been further incorporated into a complete technological process for the monolithic integration of GaAs MQW lasers and HEMT-based laser-driver circuits capable of operation in data rates up to 20 Gb/s. Using the impurity-free interdiffusion process, large shifts in the lasing wavelength have been achieved with no strain relaxation and while maintaining the high-speed modulation properties of the pseudo-morphic InGaAs/GaAs MQW lasers, demonstrating the feasibility of fabricating high-speed multi-wavelength laser arrays.

A new apparatus is proposed for the package of AlGaInP visible laser diodes (LD) in this paper. Corresponding to the metal-can used in the conventional LD apparatus, plastics and lead-frame are used in this apparatus to reduce its cost. All the chip-mounting and wire- bonding for the apparatus are also modified to accord with the requirement of simplicity and good productivity. An lead-frame with a heat-dissipation tail is specially designed to overcome the poor heat-conductivity problem, which is observed in the common plastic-molded apparatus. The life time of the AlGaInP LD using the new plastic-molded apparatus is about five times longer than that using the common one.

In this short review we describe phenomenologically what is known about laser and light emitting diodes (LEDs) degradation and review the physical understanding of it. We will then examine the issues that are relevant to the more novel vertical surface emitting lasers devices and to the new materials that are being used in the fabrication of LEDs and lasers.

Different 980 nm ridge waveguide pump laser diodes fabricated either from the InGaAs/Ga(Al)As system or from the InGaAs/Ga(In)As(P)/GaInP (Al-free) one, and purchased from different manufacturers, have been submitted to an accurate electro-optical characterization and lifetest for a comparative study. Measurements show that the electro- optical behavior, especially the kink power level and the optical spectrum, is strongly correlated with the stripe design. These different behaviors strongly impact the short term stability of both output power and wavelength of related 980 nm pump laser modules. Lifetests and failure analysis have been performed and demonstrate the vulnerability of the front facet.

For lasers modulated with a pseudo-random bit stream without prebias, the delay between the optical pulse and the current pulse depends on the number `0's preceding the current pulse (`1'). Since 1's and 0's occur `randomly' in a pseudo-random bit stream and the decision circuit is designed to start sampling at a given time, this effect results in a timing jitter. The jitter induced noise and the associated power penalty are calculated. The results suggest that the ratio of the modulation current to the threshold current of the laser should be > 25 to keep the power penalty below 1 dB at high data rates. Low threshold lasers operating without prebias are important for laser array based transmitters.

We report on the results of life testing Nichia NLPB500 blue LEDs. All tests were performed with the LEDs in a temperature controlled chamber, and all equipment operation and data collection was computer automated. The tests began with 18 newer (Nichia batch 4B0001) and two older (Nichia batch S402024, acquired a year earlier) LEDs, operated at 20 mA continuous wave (CW) and 23 degree(s)C. Light from each LED was coupled to an optical fiber and fed directly to individual photodetectors. The general trend for the 18 newer LEDs was for the output intensity to increase at a faster rate within the first 50 h and then at a slower rate over the remainder of the first test. The output intensity of the two older LEDs increased within the first 50 h then decreased during the remainder of the first 1000 h. All 20 of the LEDs in the first 1000-h test were subjected to a second 1650-h test at 23 degree(s)C and at currents ranging from 20 mA to 70 mA CW. Only one LED, an older device, suffered a soft failure during this second test. The remaining LEDs underwent a third test at 30 degree(s)C and a fourth test at 35 degree(s)C, all at various currents. We will perform failure analysis on all sufficiently degraded devices and report those results elsewhere.

The use of vertical cavity surface emitting lasers (VCSELs) in a parallel optical interconnect for Motorola's OPTOBUS^TM interconnect was made public over 1 year ago. This was the first time VCSELs were introduced into a product which took advantage of the excellent qualities of VCSELs over edge-emitting lasers. Motorola's OPTOBUS^TM interconnect is a ten channel parallel bi-directional data link based on two 10 channel multimode fiber ribbons. One of the key differences in this type of interconnect compared with previous data link designs is the use of the VCSELs as the optical source for the link's fiber optic transmitter. A single 1 X 10 VCSEL array from a GaAs wafer is die attached to a 10 channel GUIDECAST^TM optical interface unit which couples the emission from each laser device to its corresponding fiber ribbon channel and thus negates the use of expensive manufacturing techniques such as active alignment and pig-tailing. The OPTOBUS^TM interconnect achieves its performance goals (which include low cost) via the unique characteristics of the GaAs VCSELs arrays. For example, the 850 nm devices produce a circular symmetric beam with a half angle of about 10 degrees allowing the coupling loss into the waveguide to be less than 3 dB. In addition, to maintain low manufacturing costs, each VCSEL array is individually and automatically probe tested (just as in the silicon industry) to verify that each VCSEL achieves the OPTOBUS^TM interconnect's stringent electrical, optical, thermal and mechanical specifications. Typical computer generated wafer maps from automated production tooling and statistical parametric results are discussed. The combination of low threshold currents with superior thermal and optical performance allow the devices to be modulated under fixed bias conditions. Typical drive currents of 3X threshold are used to obtain nominal FDA Class 1 safety optical power levels from the GUIDECAST^TM optical interface unit.

With the growing maturation of vertical cavity surface emitting laser (VCSEL) technology as a source of commercial off-the-shelf components, the question of VCSEL suitability for use in avionics-qualifiable fiber-optic systems naturally follows. This paper addresses avionics suitability from two perspectives. First, measured performance and burn-in reliability results, determined from characterization of Honeywell VCSELs, are compared with application-based military and commercial avionics environmental requirements. Second, design guidelines for developing a cost-effective VCSEL optical subassembly (VCSEL/OSA) are outlined.

We describe vertical cavity surface emitting laser (VCSEL) reliability tests comprising hundreds of parts and more than a million device hours. The VCSELs studied were of a previously described production design intended for local-area network data communication at 850 nm. Devices were operated at temperatures of 35, 80, 100, 125, and 150 degrees C and at currents of 5, 10, 15, 20, and 30 mA, and their operating characteristics were measured at room temperature. Additional groups were operated at 225 degrees C. Nominal operation is expected to be at 40 degrees C ambient and near 10mA; stresses due to temperatures and currents above the operating range accelerated degradation. The results support an Arrhenius- type failure-acceleration model with lognormal reliability distribution and lead to an 0.88-1.2- eV estimate for the failure activation energy. When tested at room temperature, typical VCSELs exhibited initial increases in power followed by decreases. The results were essentially independent of the package type (hermetic, unsealed, or overmolded plastic). Time- lapse video of degrading devices was employed in an effort to define the failure mode, which does not appear to be mediated by dark-line defects. Under normal operating conditions the observed VCSEL reliability is equal to, or better than, typical reliability results for other AlGaAs data communications lasers or LEDs.

The use of native oxides (selective oxidation) in vertical cavity surface emitting lasers has produced dramatic improvements in these laser diodes but has also been suspected of causing poor reliability because of incidental reports of short lifetimes and physical considerations. Here we discuss the results of thousands of hours life-tests for oxide confined and implant confined devices at current densities from 1 to 12 kA/cm². There was a single infant mortality failure from a sample of 14 oxide confined lasers with the remainder showing relatively stable operation. The failed device is analyzed in terms of light current characteristics and near-field electroluminescence images, and potential screening criteria are proposed.

VCSELs have recently made a great deal of progress both in improved performance with threshold currents now < 100 (mu) A, as well as in their commercialization. Parallel communication links based on VCSEL arrays are now commercially available. However, little information has been published to date on VCSEL reliability or on what causes VCSEL failures. In this presentation, we will describe the VCSEL degradation processes observed in the wide variety of structures we have tested. These include GaAs- and InGaAs-QW VCSELs; top- and bottom-emitting structures; and proton-implanted and etched-pillar VCSELs. We will discuss the novel observation that in most VCSELs we have examined, defects in the upper mirror (a p-type Distributed Bragg Reflector) can be associated with VCSEL degradation. Laser spectra show a luminescence peak from these mirrors, indicating the presence of minority carriers in the low-bandgap layers of the mirrors. These minority carriers are thought to be at the origin of the defect formation in the p-mirrors. We will discuss the possible sources of this minority carrier injection, and present spectra which shed light on the cause of this phenomenon. We will also discuss how fabrication and packaging stresses for some structures significantly accelerate the degradation process. The failure modes observed for various designs will be shown, and possible design improvements suggested.

Broad-area stripe laser diodes based on GaAs and Al-free spacer and Al-free spacer and waveguide layers were studied and compared to conventional AlGaAs-laser diodes. The structures were grown by low pressure MOVPE (metal organic vapor phase epitaxy). For the active region InGaAs-single quantum wells with an emission wavelength of 915 nm were used. Threshold current density, internal loss and internal efficiency are comparable for the three structures under study. The use of a quaternary spacer layer instead of GaAs improves the performance for laser diodes with a low divergence ((Theta) _{perpendicular} equals 20 degree(s) FWHM). Using a non-optimized facet coating procedure about 1.2 W cw output power at a vertical divergence of (Theta) _{perpendicular} equals 26.5 degree(s) are obtained from a 50 micrometers wide stripe laser with Al-free waveguides.

In this paper MOCVD epitaxial growth of InGaAs/GaAs strained quantum well lasers lasing at (lambda) equals 1.06 mkm will be discussed. Series of Single Quantum Well Separate Confinement Heterostructures were grown with different quantum well thickness d and active layer In_xGa_1-xAs composition x. Luminescence characteristics were investigated with approaching of active layer thickness to critical value. At the near critical thickness of active layer splitting of the electroluminescence peak was observed. Also steplike changing of emitting wavelength was detected during measurements of luminescence wavelength versus active layer thickness d. Emitting characteristics and laser diodes degradation character were explored. Express selection criteria of laser structures making possible to manufacture laser diodes with lifetime more than 1000 hours at operation power 1 Watt in cw multimode regime are discussed.

In this paper we present the calculation of local mirror facet overheating of the SCH laser diode active region. It is shown that optical strength of the mirror facet prior to optical damage depends on optical confinement factor ((Gamma) -factor) and thickness of the active region layer adjacent to surface (`dead layer') where nonradiative recombination rate is much higher. Detailed investigations of local mirror facet temperature and optical strength of mirror facet in both Al-containing (AlGaAs/GaAs, InGaAs/AlGaAs/GaAs) and Al-free (InGaAsP/GaAs) single quantum well laser diodes were carried out. Experimental results are in good agreement with calculations. It is shown that optical strength of mirror facet for laser heterostructure can be derived from the behavior of local mirror facet overheating of laser diodes.