13th International Conference on Defects--Recognition, Imaging and Physics in Semiconductors: Defects in Devices
Program Organizers: Marek Skowronski, Carnegie Mellon University; Robert Stahlbush, Naval Research Laboratory; Michael Dudley, State University of New York at Stony Brook
Wednesday PM
September 16, 2009
Room: Glessner Auditorium
Location: Oglebay Resort and Conference Center
Session Chair: Jean-Pierre Landesman, Institut des Matériaux Jean-Rouxel, CNRS and Nantes University
4:00 PM Invited
Reliability Investigations on High-Power, High-Brightness Semiconductor Lasers: Ute Zeimer1; Bernd Sumpf1; Karl Häusler1; Götz Erbert1; 1Ferdinand-Braun-Institut für Höchstfrequenztechnik
High-brightness red emitting diode lasers are key devices for laser display technology. Due to the lower efficiency and higher temperature sensitivity compared to NIR diode lasers it is challenging to get the necessary requirements for reliability. Both broad area and tapered lasers emitting at 650 nm based on InGaP quantum wells embedded in AlInGaP waveguide layers are developed. These devices deliver output powers in the Watt-range. Device properties and a study of the aging behavior over several 1000h will be presented. Analysis of failed devices is carried out by optical microscopy and electro-luminescence imaging from the front facets as well as by near field measurements and wavelength resolved cathodoluminescence. The influence of mounting induced stress and operation temperature on the reliability will be discussed.
4:30 PM
Defect Imaging in Laser Diodes by Mapping Their Infrared Emission: Jens Tomm1; 1Max-Born-Institut
We report on the use of infrared emission in the 1-2 µm spectral range from diode lasers that have their primary emission in the visible or near-infrared spectral range up to 980 nm. We address the nature of this extra infrared emission from various types of GaAs-based devices. We find three additional low-energy lines of spontaneous emission assigned to bandtail-related luminescence from the gain region, and interband and deep-level-related luminescences from the GaAs substrate. With this knowledge we mapped a number of high-power diode laser arrays with respect to this type defect-related emission. Fur this purpose a thermocamera has been used while limiting the detection range to the near infrared. Both brighter and poorer emitting areas are indicative for different mechanisms that affect the reliability of the devices. The mechanisms are discussed based on the analysis of samples from different batches.
4:45 PM
Investigation of Thermal Effects in Quantum Cascade Lasers: Kamil Pierscinski1; Dorota Pierscinska1; Kamil Kosiel1; Anna Szerling1; Maciej Bugajski1; 1Institute of Electron Technology
The quantum cascade lasers (QCLs) are the most advanced class of semiconductor sources of midinfrared radiation. QCLs suffer, however, from large current densities, resulting in high active region temperatures, which make room temperature continuous wave (CW) operation still difficult to achieve. Progress in thermal management and better understanding of thermal effects are needed for further development of quantum cascade lasers. In this paper we use spatially resolved thermoreflectance (SRTR) to measure temperature distribution over the facet of pulsed operated quantum cascade lasers. The presented method gives an insight into distribution and relative importance of heat sources within the laser. It also allows for determination of thermal resistance of the laser and to evaluate the in-plane kparallel and the cross-plane kperp thermal conductivities of the active region which enables validation of a two-dimensional model for the anisotropic heat diffusion in QCLs.
5:00 PM
Investigation of Leakage Current of AlGaN/GaN HEMTs under Pinch-off Condition by Electroluminescence Microscopy: Martina Baeumler1; Michael Dammann1; Frank Gütle1; Helmer Konstanzer1; Wilfried Pletschen1; Rüdiger Quay1; Patrick Waltereit1; Michael Mikulla1; Oliver Ambacher1; Franck Bourgeois2; Franck Bourgeois2; Franck Bourgeois2; Reza Behtash2; Klaus Riepe2; Paul J. van der Wel3; Jos Klappe3; Thomas Rödle3; 1Fraunhofer Institut für Angewandte Festkörperphysik; 2United Monolithic Semiconductors; 3NXP Semiconductors
Reduction of leakage currents under pinch-off conditions is necessary to improve the high voltage and long term stability of AlGaN/GaN HEMTs. We will present results from on-wafer electroluminescence (EL) microscopy on devices with leakage currents (Ileak) varying over four orders of magnitude. The EL images reveal a small band of enhanced EL along the drain side of the gate finger. We will demonstrate that in the off-state region the integrated EL intensity is proportional to Ileak independent of gate width for the devices under study. Plotting EL intensity as a function of gate voltage supports that below threshold the EL intensity follows the Ileak(UG)-dependence. The EL(UG) dependencies for positions of high and low EL intensity allow to identify areas of enhanced leakage currents for FIB cross-sections. Results after electrical stress will be discussed based on the question whether areas of enhanced leakage current have an impact on the degradation phenomena.
5:15 PM
Defect Formation in Electrically Degraded GaN High Electron Mobility Transistors: Lingjia Li1; Marek Skowronski1; 1Carnegie Mellon University
In spite of their extraordinary performance, the wide spread use of AlGaN/GaN high electron mobility transistors is delayed by reliability issues. It has been found that device characteristics, such as gate current, drain current, and output power, degrade after high electric field DC stress. Electroluminescence images suggest non-uniform degradation along the gate with the formation of radiative recombination centers. Cross-sectional transmission electron microscopy performed at degradation sites revealed the formation of a pit-shaped defect at the drain-side edge of the gate during stress, accompanied by a crack-like defect extending from the bottom of the pit into the AlGaN/GaN epilayers. This observation is consistent with a defect formation mechanism associated with excessive inverse piezoelectric stress. These defects degrade device performance by trapping electrons and assisting electron tunneling between gate and channel, resulting in reduction of the sheet carrier concentration of the channel and lowering the Schottky barrier height of the gate.
5:30 PM
Detection of Device-Process Induced Extended Defects in 4H-SiC: Masahiro Nagano1; Hidekazu Tsuchida1; Takuma Suzuki2; Tetsuo Hatakeyama2; Junji Senzaki3; Kenji Fukuda3; 1CRIEPI; 2R&D Association for FED; 3AIST
The detection of device-process induced extended defects in 4H-SiC during the ion-implantation/activation-anneal process was investigated by comparing synchrotron reflection X-ray topography images taken before and after the process. Aluminum, nitrogen and phosphorus ions were implanted and the annealing process was performed at 1670ºC. We have succeeded in detecting the formation of extended defects induced by the process, the formation modes of the extended defects are classified into (i) the generation of Shockley-type stacking faults near the surface of the epilayers, (ii) the generation of the BPD half-loops with interfacial dislocations near the epilayer/substrate interface, (iii) the migration of the preexisting BPDs with generation of dislocations near the implanted-layer/epiplayer interface or (iv) near the epilayer/substrate interface.
5:45 PM
Strain Mapping and Its Effect on Electrical Properties in Hetero-Structured AlGaN/GaN Devices: Nadeemullah Mahadik1; Syed Qadri2; Mulpuri Rao1; 1George Mason University; 2Naval Research Laboratory
Point-wise high resolution x-ray measurements were performed on AlGaN/GaN wafer to study the effect of localized strain on the transport measurements across the wafer. A whole wafer strain map of the AlGaN/GaN HEMT wafer showed a one-to-one correspondence with the variation in electrical resistivity. The in-plane strain variation is in the range of 2.295x10-4 – 3.539x10-4 resulting in a sheet resistance variation of 345 - 411 Ω/sq. Additionally, in-situ x-ray diffraction measurements, performed on AlGaN/GaN device structures under variable bias conditions, showed tensile strain for forward bias conditions, and compressive strain for reverse bias. Since the AlGaN/GaN interface has a high degree of piezoelectric polarization, these measurements were correlated with a variation of piezoelectric charges at the interface. A linear variation in the strain was observed with the bias voltage, which results in a change in the piezoelectric charge at the AlGaN/GaN interface with bias.
6:00 PM
Imaging the Catastrophic Optical Mirror Damage in High-Power Diode Lasers: Mathias Ziegler1; Jens Tomm2; Thomas Elsaesser2; Ute Zeimer3; 1Max-Born-Institut ; 2Max-Born-Institut; 3Ferdinand-Braun-Institut für Höchstfrequenztechnik
We report on the combination of thermography and near-field imaging for monitoring the catastrophic optical mirror damage (COMD) of red- and infrared-emitting high-power broad-area diode lasers operating in cw and single-pulse mode. Thermography is highly COMD-selective since it has the unique capability of directly imaging the abrupt threshold-like device-temperature increase during the thermal runaway and subsequent melting processes, appearing as a “thermal flash”. From monitoring the near-field pattern we can anticipate potential COMD locations and follow the damage-induced loss in laser intensity. Additional analysis with scanning-electron microscopy and cathodoluminescence links to the COMD-induced structural changes at the facet and in the volume. All techniques exhibit strong correlations in COMD location and strength, and, because of the thermal flash, allow for an unambiguous decision about the COMD occurrence, also in situations of competing degradation mechanisms. Applied in concert, the approach enables for deeper insight into the physics behind COMD.