Gaas-based High-temperature Hbt Devices And Their Characteristics

Due to their excellent high-frequency performance, GaAs-based heterojunction bipolar transistors (HBTs) are promising devices for microwave and millimeter wave application. With the development of the integrate circuits and increasing of the integration, transistors in the chip are facing the challenge of high-temperature and/or high-power applications. For their higher handgap discontinuity ( Eg ),AlGalnP/GaAs HBTs are very promising devices for use in power application under high-frequency conditions. However, The former reports show that AlGalnP/GaAs HBTs can't operate up to their highest temperature in theory, because of the reliability of device's ohmic contact. In this work, the DC and temperature characteristics GaAs-based high-temperature heterojunction bipolar transistors are studied.Different failure mechanisms of GaAs-based HBT have been discussed. To improve GaAs-based HBT's reliability, thermally stable ohmic contacts of Mo/W/Ti/Au and Ti/W/Ti/Au were fabricated us ng (NH4)2S passivation and rapid thermal annealing. The characteristics of this structure behaved in ohmic-junction characteristics, indicating that (NH4)2S passivation eliminated Fermi level pinning. Electrical measurement showed a minimum ohm c contact resistivity of 10-6 cm2 . The electrical and structural properties of ohmic contacts were studied by measuring the contact resistivity and analyzing Auger Energy Spectrum (AES) and X-rayDiffraction (XRD).In order to fully understand the influence cf temperature on characteristics in HBT, a high-temperature HBT model has been established. In this model, the variations of BC junction reverse current with temperature and applied voltage have been taken into account. "Soft breakdown" phenomenon at high temperature can be simulated with model. In addition, a new thermal distribution model is developed in this study on the basis of work done by others.For GaAs-based DHBT, the potential spike of B-C heterojunction is a significantfactor in determining the collector-emitter saturation voltage. In this work, the undoped GaAs layer has been employed at the B-C heterojunction to avoid the undesired electron blocking effect. This result shows that the collector-emitter saturation voltage decreases from 3V to 0.6V. We think that this phenomenon is mainly caused by the absence of potential spike at the B-C heterointerface due to the insertion of the i-GaAs layer. So at the B-C heterojunction, for the forward-biased condition, electrons can be injected directly from the emitter into base and the collector in spite of the existence of These results collectively indicate that theelectron blocking effect is indeed removed in the studied device.A novel high-temperature HBT with thermally stable ohmic contacts has been proposed and fabricated to obtain temperature performance for power amplifier. In this device, Mo/W/Ti/Au has been used for emitter contact metal instead of AuGeNi and Pt diffusion barrier has been inserted into base contact metal Ti/Au. This studied HBT device can stably work in range from room temperature to 673K. Device's B-E and B-C junction diode properties at different temperatures have been studied. It shows that the thermal stability of the ohmic contacts is key factor of the high-temperature characteristics for GaAs-based HBT.