The thermal characteristics of 808 nm Al Ga As/Ga As laser diodes（LDs） are analyzed via electrical transient measurements and infrared thermography. The temperature rise and thermal resistance are measured at various input currents and powers. From the electrical transient measurements, it is found that there is a significant reduction in thermal resistance with increasing power because of the device power conversion efficiency. The component thermal resistance that was obtained from the structure function showed that the total thermal resistance is mainly composed of the thermal resistance of the sub-mount rather than that of the LD chip, and the thermal resistance of the sub-mount decreases with increasing current. The temperature rise values are also measured by infrared thermography and are calibrated based on a reference image, with results that are lower than those determined by electrical transient measurements. The difference in the results is caused by the limited spatial resolution of the measurements and by the signal being captured from the facet rather than from the junction of the laser diode.
The effect of drain-source voltage on A1GaAs/InGaAs PHEMTs thermal resistance is studied by experimental measuring and simulation. The result shows that A1GaAs/InGaAs PHEMTs thermal resistance presents a downward trend under the same power dissipation when the drain-source voltage （VDs） is decreased. Moreover, the relatively low VDS and large drain-source current （IDs） result in a lower thermal resistance. The chip-level and package-level thermal resistance have been extracted by the structure function method. The simulation result indicated that the high electric field occurs at the gate contact where the temperature rise occurs. A relatively low VDS leads to a relatively low electric field, which leads to the decline of the thermal resistance.
We examined the wake-up effect in a Ti N/Hf_(0.4)Zr_(0.6)O_(2)/TiN structure.The increased polarization was affected by the cumulative duration of a switched electric field and the single application time of the field during each switching cycle.The space-charge-limited current was stable,indicating that the trap density did not change during the wake-up.The effective charge density in the space-charge region was extracted from capacitance-voltage curves,which demonstrated an increase in free charges at the interface.Based on changing characteristics in these properties,the wake-up effect can be attributed to the redistribution of oxygen vacancies under the electric field.
The effects of self-heating and traps on the drain current transient responses of AlGaN/GaN HEMTs are studied by 2D numerical simulation. The variation of the drain current simulated by the drain turn-on pulses has been analyzed. Our results show that temperature is the main factor for the drain current lag. The time that the drain current takes to reach a steady state depends on the thermal time constant, which is 8μs in this case. The dynamics of the trapping of electron and channel electron density under drain turn-on pulse voltage are discussed in detail, which indicates that the accepter traps in the buffer are the major reason for the current collapse when the electric field significantly changes. The channel electron density has been shown to increase as the channel temperature rises.
The phenomenon of self-changing on the device parameters and characteristics after a step voltage stress was applied to the gate is studied in A1GaN/GaN high electron mobility transistors. The device was measured every 5 rain after the stress was removed. The large-signal parasitic source （drain） resistance, transfer characteristics, threshold voltage, drain-source current, gate-source （drain） reverse currenwvoltage characteristics changed spontaneously after the removal of the stress. The time constant of tile self-changing was about 25 27 rain. The gate-source （drain） capacitance-voltage characteristics were constant during this process. Electrons were trapped by the surface states and traps in the AIGaN barrier layer when the device was under stress. The traps in the AIGaN barrier layer then released electrons in less than 10 s. The surface states released electrons continuously during the entire measurement stage, leading to the self-changing of mearsurement result.
