Yanbin Qiao

Spatial hole burning degradation of AlGaAs/GaAs laser diodes

The degradation of AlGaAs/GaAs laser diodes is studied in detail using laser scanning confocal microscopy, cathodoluminescence images, and x-ray diffraction (XRD) techniques. Our analysis has identified a degradation mechanism that results from the periodic distribution of the carrier density and the near-field intensity originating from periodic spatial hole burning. Based on the XRD measurements, we find that the epitaxial layer enters a polycrystalline phase during degradation due to the dark line defects, and the out-of-plane strain and in-plane compressive stress are induced by degradation.

Working Thermal Stresses in AlGaAs/GaAs High-Power Laser Diode Bars Using Infrared Thermography

An interesting approach is proposed for investigating the thermal stress of AlGaAs/GaAs laser diode bars using infrared thermography. We obtained horizontal and perpendicular profiles of the working thermal stress through the active region in one emitter (emitter 5) at operating currents 0.5 and 1.0 A. The thermal stress at the center of emitter 5 is found to quickly rise to values 2.1 and 3.4 MPa under the operating currents 0.5 and 1.0 A. The thermal stress gradient in the epitaxial layer is also larger than that in the substrate. In addition, if emitter 5 operates individually, a thermal stress spike at a current of about 0.2 A appears, with a sharper rise in slope between 0.1 and 0.2 A than between 0.2 and 1.0 A. Furthermore, with regard to the properties of transient working thermal stress, the profile of the thermal crosstalk between emitters was obtained at different operating currents.

Cycled Thermomechanical Failure in 808-nm High-Power AlGaAs/GaAs Laser Diode Bars

Thermomechanical cycle failure was analyzed in 808-nm high-power AlGaAs/GaAs laser diode bars (LDBs) in detail. Two thermal stress cycle experiments were carried out in these devices with peak thermal stresses of 19.4 and 33 MPa. The threshold current increase demonstrated a square-root dependence on the cycle number, and a tail and split in lasing spectrum were observed. This result was attributed to nonradiative recombination increasing with cycle number due to the diffusion of defects that accompanies band-structure renormalization. Furthermore, from X-ray diffraction measurements we found that the epitaxial layer remains monocrystalline during thermal stress cycling. We calculated the out-of-plane strain and in-plane stress induced by plastic deformation in the epitaxial layer based on the interplanar spacing in the crystal. Our results suggest that thermomechanical strain and stress were induced by pulsed operation, which led to degradation of the high-power LDBs.

The impact of the stress induced by lateral spatial hole burning on the degradation of broad-area AlGaAs/GaAs laser diodes

The degradation of broad-area AlGaAs/GaAs laser diodes is studied experimentally and theoretically in detail, and we suggest a degradation mechanism associated with the stress which originates from the lateral spatial hole burning (SHB) effects. Our analysis shows that thermal stresses have critical effects on the degradation of laser diodes, which are induced by increased local heating by nonradiative recombination and self-absorption of photons originating from the lateral SHB within the laser diode during degradation. Such results are confirmed by the simulation using the software lastip. Furthermore, the average values of the induced thermal strain and stress by lateral SHB are 0.00063 and 85 MPa, respectively, through the x-ray diffraction measurement. The stress exceeds that for the initiation of plastic deformation (as calculated to be approximately 40–50 MPa based on the finite element method), thus, suggesting that plastic deformation has occurred within the cavity due to the lateral SHB effect d...

Thermal resistance analysis related to the degradation of GaAs-Based laser diodes

Thermal transient measurement of the 808 nm GaAs-Based laser diodes (LDs) before and after the constant current stress are presented and discussed in this paper. Aging tests are carried out under the conditions of the constant current stress (1 A) for 255 hours. The total thermal resistance increases from 7.0 to 8.8 °C/W before and after degradation. Furthermore, the contribution of each component to the total thermal resistance has been obtained from the differential structure function and cumulative structure function before and after stress. The thermal resistance of chip maintain almost constant before and after stress, while significant increase in the thermal resistance of solder layer (indium attaching material) and package body are observed after degradation. These results indicate that the thermal properties of solder layer and package body degrade apparently as contrast to the chip of LDs. The thermal properties of solder layer and package body have critical effects on the performance of LDs. Thus the performance of LDs could be improved through optimizing of solder material and package body.

Reliability of solder joints in High-power LED package in power cycling tests

In this paper, an improved method to investigate the reliability of solder joint between High-power LED chip and heat sink is presented. The power cycling is carried out through the switching on and off of the current stress. The optical and electrical characteristics do not degrade apparently. Electrical method is used to measure the thermal resistance of high-power LED which increases from 15.81°C/W to 43.95°C/W for typical one of three samples before and after power cycling. Furthermore, some voids are observed in solder joint after power cycling according to the result of scanning acoustic microscope (SAM). That is, the solder joint degrade significantly after power cycling. Our results indicate that this method can effectually evaluate the reliability of solder joint.

Study of Heat Transport Behavior in GaN-Based Transistors by Schottky Characteristics Method

The dynamic behavior of the thermal transport characteristics in the active region of AlGaN/GaN transistors was investigated experimentally. The transient temperature rise, the sectional temperature distribution, and the heat transport characteristics were all measured using the Schottky gate junction voltage characteristics method. The results show that three steps were observed in the transient temperature rise and/or Schottky gate voltage drop curves. The transient temperature rise behavior at different positions in the active region under various power conditions is discussed in detail. In addition, the heat transport delay in the active region of the AlGaN/GaN transistors is also studied. The results indicated that the transport velocity of the heat is 1.47 m/s. This is important when changes occur to the electrical characteristic parameters of the device, because any heat transport-related delay would also induce associated delays in the changes to the electrical characteristic parameters in the AlGaN/GaN transistors.

Investigation of Electromigration Degradation Mechanism in Ti/Pt/Au Ohmic Contacts to p-GaAs Under High Current Density Stress

The degradation mechanism of Ti/Pt/Au ohmic contacts to p-GaAs was identified experimentally under high direct-current density stress in detail. A revised measuring structure was designed based on the circular transfer length method (CTLM), in which the high current density of

Thermal distribution measurement on FPGA using optimized ring oscillator (RO)-based thermal sensor network

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Reliability evaluation of Schottky contact of AlGaN/GaN HEMT, based on two AC voltages with different frequencies

A/cm2 was applied vertically, while the contact resistance was measured horizontally between two contact electrodes. According to revised CTLM, the specific contact resistance was measured during stress. The results indicated that specific contact resistance showed an exponential dependence on the aging time. The depth profiling results obtained from the Auger electron spectroscopy showed that Pt penetrated into the Au layer during stress. Furthermore, some voids were observed at the Au/Pt interface, and intermixing began to form within metal layer during stress. These results demonstrated that the degradation of Ti/Pt/Au ohmic contacts to p-GaAs was attributed mainly to the electromigration and Joule heating along the current direction under high current density.