[Show abstract][Hide abstract] ABSTRACT: Electroluminescence (EL) spectroscopy in combination with drift-diffusion simulations was used to prove the presence of impact ionisation in AlGaN/GaN HEMTs illustrated on InGaN back-barrier devices. Regardless of the level of gate leakage current, which is dominated by contributions such as surface leakage current and others, EL enabled the revealing of hole generation due to impact ionisation. Hole currents as low as 10pA were detectable by the optical technique used.
[Show abstract][Hide abstract] ABSTRACT: A thermal boundary resistance (TBR) is associated with the presence of an AlN nucleation layer (NL) in AlGaN/GaN high-electron-mobility transistors (HEMTs) grown on SiC substrates, raising device temperature beyond what is expected from the simple thermal conductivities of the main device layers. TBR was found to differ by up to a factor of four between different device suppliers, all using standard metal-organic chemical vapor deposition (MOCVD) growth techniques, related to the detailed NL microstructure. Optimizing the NL crystalline structure in MOCVD could therefore significantly improve heat extraction from AlGaN/GaN HEMTs into the SiC substrate, potentially reducing peak channel temperature rise by up to 40%, significantly benefiting device reliability.
[Show abstract][Hide abstract] ABSTRACT: A new methodology is developed to determine spatial location and properties of traps generated by electrical stressing of AlGaN/GaN high-electron mobility transistors, based on integrated optical and electrical analysis. Mild off-state stress increases irreversibly the number of traps located in the near-surface AlGaN region at the gate edge. A deep level with 0.45-eV activation energy in fresh devices changes its nature to interacting defect after the off-state stress, accompanied by an activation energy change. These results are consistent with trap generation in the near-surface AlGaN region at the gate edge related to high electric field and gate leakage current, as stressing does not result in the generation of cracks in the AlGaN layer.
[Show abstract][Hide abstract] ABSTRACT: Photoluminescence (PL) spectroscopy was used to determine lateral temperature distributions in AlGaN/GaN based devices. Results are compared to Raman thermography data and to thermal modeling to assess challenges in the determination of temperature in devices using PL analysis and corresponding solutions. In conjunction with Raman thermography, the vertical temperature distribution in the devices is determined and the thermal boundary resistance at the GaN/SiC interface extracted.
[Show abstract][Hide abstract] ABSTRACT: Raman spectroscopy, utilizing both the GaN E <sub>2</sub> and A <sub>1</sub>( LO ) phonon modes, has been used to simultaneously probe temperature and thermal stress in operating AlGaN/GaN high electron mobility transistors (HEMTs). Temperature and thermal stress profiles across the active region of an AlGaN/GaN HEMT were determined. The results were found to be in good agreement with thermal and thermomechanical simulations. The maximum temperature rise and thermal stress measured in the GaN layer are located close to the drain edge of the gate contact, reaching 240 ° C and -0.37 GPa, respectively, for a power dissipation of 25 W/mm (40 V).
[Show abstract][Hide abstract] ABSTRACT: We report on the development of a integrated Raman - IR thermography technique to probe self-heating in active devices. We compare and discuss advantages of both techniques in terms of spatial resolution on the example of AlGaN/GaN HFET devices. While traditional infra-red (IR) thermography can provide fast overviews of self-heating in the devices over large scales, its use for extraction of channel temperatures is limited by the sub-micron size of the active area in modern devices. Integration with micro-Raman thermography provides not only improvement in spatial resolution down to 0.5 mum on the surface but also unprecedented micron scale depth resolution for true 3D thermography. This enables unique thermal analysis of semiconductor devices on a detailed level not possible before. As it is a generic technique its application can be extended to Si, GaAs and other devices. This opens new opportunities for device performance and reliability optimization, and failure analysis in research and development of modern semiconductor technology, as well as for quality control/ manufacturing environments.
Physical and Failure Analysis of Integrated Circuits, 2008. IPFA 2008. 15th International Symposium on the; 08/2008
[Show abstract][Hide abstract] ABSTRACT: Time-resolved Raman thermography, with a temporal resolution of , was used to study the thermal dynamics of AlGaN/GaN electronic devices (high-electron mobility transistors and ungated devices). Heat diffusion from the device active region into the substrate and within the devices was studied. Delays in the thermal response with respect to the electrical pulse were determined at different locations in the devices. Quasi-adiabatic heating of the AlGaN/GaN devices is illustrated within the first of device operation. The temperature of devices on SiC was found to reach of the dc temperature when operated with -long electrical pulses.
[Show abstract][Hide abstract] ABSTRACT: The influence of a thermal boundary resistance (TBR) on temperature distribution in ungated AlGaN/GaN field-effect devices was investigated using 3-D micro-Raman thermography. The temperature distribution in operating AlGaN/GaN devices on SiC, sapphire, and Si substrates was used to determine values for the TBR by comparing experimental results to finite-difference thermal simulations. While the measured TBR of about 3.3 x 10<sup>-8</sup> W<sup>-1</sup> ldr m<sup>2</sup> ldr K for devices on SiC and Si substrates has a sizeable effect on the self-heating in devices, the TBR of up to 1.2 x 10<sup>-8</sup> W<sup>-1</sup> ldr m<sup>2</sup> ldr K plays an insignificant role in devices on sapphire substrates due to the low thermal conductivity of the substrate. The determined effective TBR was found to increase with temperature at the GaN/SiC interface from 3.3 x 10<sup>-8</sup> W<sup>-1</sup> ldr m<sup>2</sup> ldr K at 150degC to 6.5 x 3.3 x 10<sup>-8</sup> W<sup>-1</sup> ldr m<sup>2</sup> ldr K at 275degC, respectively. The contribution of a low-thermal-conductivity GaN layer at the GaN/substrate interface toward the effective TBR in devices and its temperature dependence are also discussed.
[Show abstract][Hide abstract] ABSTRACT: We review our latest developments in the field of Raman thermography and its application to GaN microelectronics. Device self-heating, the temperature rise in a device generated by electrical power dissipation, plays an important role for device performance and reliability, however, is difficult to assess as it occurs on sub-micrometer length scales in most devices, not observable using traditional thermography techniques. The new technique of Raman thermography enables to gain unprecedented insight into device self-heating with sub-micron spatial and with nanosecond time resolution. Thermal resistance of GaN electronic devices on different substrates and with different layouts are compared, interface thermal resistance between the GaN and the substrate was determined. Temperature measurements in the device plane and three dimensionally from the device into the substrate are discussed. Temperature in devices operated in pulsed mode as function of time, dependent on duty cycle and pulse length was studied. A comparison to temperature measurements performed using electrical methods illustrates that care must be taken when identifying junction temperatures using electrical methods.
[Show abstract][Hide abstract] ABSTRACT: Self-heating in multifinger GaAs pseudomorphic-HEMT devices was investigated by micro-Raman spectroscopy. The device temperature was probed on the die as a function of applied bias, external heating, and device geometry. The temperature of the top GaAs layer was recorded inside the source-drain gap, as well as on the device periphery using 488-nm laser excitation. Obtained Raman temperatures were found to be higher than infrared thermography results, which is due to the improved spatial resolution of micro-Raman spectroscopy. Thermal resistance and crosstalk in the multifinger devices was evaluated as a function of thermal stress and finger pitch.
IEEE Transactions on Electron Devices 09/2007;
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