Comparative study on thermal robustness of GaN and AlGaN/GaN MOS devices with thin oxide interlayers (original) (raw)
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Thermal Stability of Electrical Properties in AlGaN/GaN Heterostructures
Japanese Journal of Applied Physics, 2004
An annealing study of an AlGaN/GaN two-dimensional electron gas structure was conducted in combination with measurements of precise epitaxial layer thickness and AlGaN crystal quality. We found that the sheet resistance (R sheet) increases significantly for samples with a less-than-180-A-thick AlGaN layer when annealing is performed below the growth temperature. The R sheet increase also depends on the GaN thickness, which determines AlGaN crystal quality. Hall measurements revealed that the decrease in sheet carrier density is responsible for the R sheet increase. One possible explanation for the R sheet increase is that Si donors in poor-surface-morphology AlGaN layers are passivated or compensated from the top surfaces upon annealing. These results have a great impact on wafer selection, device process, design, and performance for short-gate AlGaN/GaN high-electron-mobility transistors.
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Gallium nitride (GaN) has attracted considerable interest for electronic device applications at high temperature environment with high power conditions. The large lattice mismatch and the large thermal expansion coefficient difference between the GaN film and silicon substrate makes it difficult to get film of high quality and suitable for the metal-oxidesemiconductor (MOS) devices. However, deposited films can be subjected to different fabrication processes to exhibit good electrical characteristics. In this paper, we report on the fabrication and characterization of MOS capacitor based on GaN grown on silicon substrates at low growth temperatures (200 and 600°C). The roughness, morphology, composition and crystalline quality of the GaN films were determined by atomic force microscopy (AFM), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and X-ray diffraction (XRD) measurements. The fabricated MOS structures were characterized using capacitance-voltage (C-V) measurements.
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Micro-Raman thermography, microphotoluminescence spectroscopy, and thermal simulation were used to study the thermal properties of AlGaN/GaN heterostructure field-effect transistors grown on semi-insulating bulk GaN substrates. A bulk GaN thermal conductivity of 260 was determined from temperature measurements on operating devices in combination with finite-difference thermal simulations. This is significantly higher than typical thin GaN epilayer thermal conductivities, due to a lower dislocation density in bulk GaN. Despite the thermal conductivity of bulk GaN being lower than that of SiC, transistors on bulk GaN exhibited a similar thermal resistance as GaN-on-SiC devices, attributed to the absence of a thermal boundary resistance between the device epilayers and substrate for GaN-on-GaN devices.
Journal of Applied Physics, 2005
The performance of AlGaN / GaN heterostructure field-effect transistors ͑HFETs͒ with either uncapped surfaces or with low-temperature ͑LT͒ GaN or SiO 2 or SiN x as gate insulators is reported. The sheet carrier concentrations of AlGaN / GaN HFETs with any of these surface insulating layers are similar to each other and in each case about 50% higher than that in an AlGaN / GaN HFET with a free surface. This result is consistent with the insulator layers providing passivation of surface states that cause the depletion of the channel layer. Due to the closer lattice match with the AlGaN surface layer, the HFET with a LT-GaN layer as the gate insulator shows the best dc and rf device performance, demonstrating that this material is an effective insulator for nitride electronic devices.
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2005 IEEE Conference on Electron Devices and Solid-State Circuits, 2005
The effects of oxidation temperature on thermally oxidized GaN film were investigated. The GaN wafers were oxidzied at 750 DC, 800°C and 850°C respectively. The electrical characteristics and interface quality of MOS capacitors were compared among different oxidation temperatures. The sample oxidized at 800°C presented best current-voltage, capacitance-voltage characteristics and smoothest surface morphology, while the higher oxidation temperature of 850°C gave best interface quality. The electrical breakdown field was increased by one order of magnitude when the sample was oxidized at 800°C as compared with 750°C and 850 DC. Lastly, after the sample oxidized at 800°C was annealed at 850°C for 10 min, the quality of its oxide was significantly degraded.
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The effect of surface treatment on the interfacial properties between the Al 2 O 3 gate dielectric and the recess-etched GaN surface of the AlGaN/GaN-based MOSFET has been characterized by capacitance-voltage (C-V) measurements. The recessed GaN surface was treated in the tetramethylammonium hydroxide (TMAH) solution at 85°C for 10 min to smoothen the surface and remove the plasma damage. The surface treatment decreases the interface trap density by removing surface traps related to the native surface oxide such as Ga x O y , which results in much improved C-V characteristics.
Effects of Self-Heating on Performance Degradation in AlGaN/GaN-Based Devices
IEEE Transactions on Electron Devices, 2000
A self-consistent electrothermal transport model that couples electrical and thermal transport equations is established and applied to AlGaN/GaN device structures grown on the following three different substrate materials: 1) SiC; 2) Si; and 3) sapphire. Both the resultant I-V characteristics and surface temperatures are compared to experimental I-V measurements and Raman spectroscopy temperature measurements. The very consistent agreement between measurements and simulations confirms the validity of the model and its numerical rendition. The results explain why the current saturation in measured I-V characteristics occurs at a much lower electric field than that for the saturation of electron drift velocity. The marked difference in saturated current levels for AlGaN/GaN structures on SiC, Si, and sapphire substrates is directly related to the different self-heating levels that resulted from the different biasing conditions and the distinctive substrate materials.
Reducing Thermal Resistance of AlGaN/GaN Electronic Devices Using Novel Nucleation Layers
IEEE Electron Device Letters, 2000
Currently, up to 50% of the channel temperature in AlGaN/GaN electronic devices is due to the thermal-boundary resistance (TBR) associated with the nucleation layer (NL) needed between GaN and SiC substrates for high-quality heteroepitaxy. Using 3-D time-resolved Raman thermography, it is shown that modifying the NL used for GaN on SiC epitaxy from the metalorganic chemical vapor deposition (MOCVD)-grown standard AlN-NL to a hot-wall MOCVD-grown AlN-NL reduces NL TBR by 25%, resulting in ∼10% reduction of the operating temperature of AlGaN/GaN HEMTs. Considering the exponential relationship between device lifetime and temperature, lower TBR NLs open new opportunities for improving the reliability of AlGaN/ GaN devices.