Dislocations in strained-layer epitaxy : theory, experiment, and applications

This chapter describes studies on the reliability of semiconductor optical devices over more than three decades, dating back to the early 1970s, focusing on gradual degradation First, three main degradation modes for optical devices, rapid degradation, gradual degradation, and catastrophic failure, are outlined (see also Chaps 1 and 5) Next, the results of the classical research into rapid degradation that was carried out in the 1970s and 1980s are presented as an introduction to a systematic discussion of the research that followed—remarkable research into gradual degradation Then, we discuss the influence of local strain to the gradual degradation and methods for eliminating the gradual degradation rate

Reliability and Degradation of III-V Optical Devices Focusing on Gradual Degradation

Semiconductor lasers are the most efficient man-made narrow-band light sources and convert up to three-quarters of electric energy into light High-power diode lasers are characterized by very high internal power densities in their small cavity, resulting in local heating and sometimes device degradation Catastrophic optical damage (COD) of diode lasers is a relevant degradation mechanism and limit for reaching ultra-high optical powers An overview is given on research activities targeting the mechanisms being relevant for the COD process in GaAs-based diode lasers emitting in the 630―1100 nm range The discussion of experiments, where COD is artificially provoked, represents the main topic The sequence of events and fast kinetics taking place on a nanosecond to microsecond time scale are addressed A particular emphasis is laid on recent experimental work performed in the authors' laboratories Paving the way for knowledge-based solutions towards more robust diode lasers represents the ultimate goal of this work COD diagram determined for a batch of broad-area AlGaAs diode lasers The time to COD within a single current pulse is plotted versus the actual average optical power in the moment when the COD takes place Full circles stand for clearly identified COD events (right ordinate), whereas open circles (left ordinate) represent the pulse duration in experiments, where no COD has been detected A borderline (gray) exists between two regions, i e, parameter sets, of presence (orange) and absence of COD (blue) This borderline is somewhat blurred because of the randomness in filamentation of the laser nearfield and scatter in properties of the involved individual devices

Mechanisms and fast kinetics of the catastrophic optical damage (COD) in GaAs-based diode lasers

Catastrophic optical damage (COD) in Al-free InGaAs/InGaP 0.98 μm lasers has been investigated using real-time electroluminescence (EL) and transmission electron microscopy (TEM). From EL images, we observed that multiple bright spots initiated from one of the facets and then propagated to the center of the cavity during the COD process. It is clarified by the TEM analysis that the propagation of bright spots resulted in 60-nm-wide Moire fringe along the cavity and the crystalline phase of the active area became polycrystalline. Highly nonradiative polycrystalline phase of the active area is the major cause of COD failure in the Al-free 0.98 μm lasers.

Characterization of catastrophic optical damage in Al-free InGaAs/InGaP 0.98 μm high-power lasers

Various types of InP-based semiconductor lasers, Fabry–Perot (FP), and distributed feedback (DFB), in different wavelength regions of 1.3, 1.48, and 1.55 μm have been subjected to human-body-model electrostatic discharge (ESD) testing. The reverse V-I characteristics of these diode lasers were found to be generally most sensitive in detecting ESD damage than the forward characteristics (e.g., threshold current) of the laser. The laser ESD failure voltages were much lower for the reverse than the forward polarity and DFB lasers were found to be more vulnerable to ESD than FP lasers. The failure mechanism was found to be due to localized melting—a thermal effect—in both polarities of ESD testing. We also report the study of the latent ESD effects on the long-term aging rates of semiconductor lasers.

Semiconductor laser damage due to human-body-model electrostatic discharge

Channeled-substrate buried heterostructure (CSBH) lasers which were purged from populations undergoing high reliability qualification have been studied in detail. Gradual and rapid degradation mechanisms leading to accelerated aging failure modes have been analyzed by transmission electron microscopy, convergent beam electron diffraction, electroluminescence, energy dispersive x-ray analysis, and chemical etching. The gradual degradation mode of CSBH lasers is characterized by (1) a gradual increase in room-temperature threshold current; (2) a decrease in external quantum efficiency, typically a drop in peak value of dL/dI greater than 25%; (3) a drop in forward voltage at low current, indicating a change in junction characteristics; (4) a large peak inI(dV/dI) below threshold (at around 3 mA); and (5) an enhancement in the peak in I2(d2V/dI2) at laser threshold. A defect mechanism associated with the gradual degradation begins with a nucleation of extrinsic dislocation loops along the V-groove {111} p-n–type sidewall interfaces between the Cd-diffused p-InP and liquid-phase-epitaxial-grown n-InP buffer inside the groove. These dislocation loops subsequently grow out of the interfaces into the n-InP buffer region in the direction of minority-carrier injection, indicating a nonradiative recombination-assisted defect growth process. For those loops which enter the quaternary active region near the tip of the active crescent, the growth rate along the (001) and (010) planes is greatly enhanced and the loops eventually cut across the active stripe and become dark-line defects, as confirmed by electroluminescence. Nucleation of dislocation loops is not observed along the {111} p-p–type sidewall interfaces above the active stripe. The fact that the dislocation loops are all extrinsic in nature implies that the {111} sidewall interfaces as well as the quaternary active region contain a high density of interstitials. The possible causes for the generation and growth of the dislocation loops and the high density of point defects are discussed. The rapid degradation mode of the CSBH laser is characterized by a sudden drop in light intensity during the aging process. The associated defect mechanism starts with localized melting at the mirror facet or inside the lasing cavity. A metal-rich droplet subsequently forms which propagates along the center of the active stripe in the direction towards the cavity center via a meltback-regrowth process; i.e., material melts in front of the droplet and regrows after it propagates by. The nonideal condition of regrowth results in the formation of a wormlike defect composed of a cylinder of defective materials bounded by an off-stoichiometric interface. The wormlike defect is dark under electroluminescence. Complicated dislocation structures can also be grown from the wormlike defect under a nonradiative recombination-assisted defect growth process. These phenomena are presented and discussed.

Defect mechanisms in degradation of 1.3-μm wavelength channeled-substrate buried heterostructure lasers

An InP/InGaAsP laser‐monitor hybrid structure which demonstrates the use of channeled‐substrate buried‐heterostructure lasers or broad area double heterostructure devices as ‘‘on‐board’’ edge‐detecting back‐face monitors is presented. Devices with and without antireflection facet coatings are used as monitors. A linear relationship between photocurrent and light output from the laser is observed for all monitor types. A photocurrent of 17.6 μA/mW is obtained with a facet‐coated, broad area monitor (at a monitor‐laser separation of ≊100 μm). The sensitivities obtained are in close agreement with those predicted assuming close to unity quantum efficiency in the junction region. Improved chip placement precision could permit a possible doubling of the monitor sensitivity.

B. P. Segner

Papers

Defect mechanisms in degradation of 1.3-μm wavelength channeled-substrate buried heterostructure lasers

InP/InGaAsP lasers with broad area double heterostructure lasers as back‐face monitors