Papers by Keyword: AlGaN

Abstract: This paper introduced an accurate empirical model for the thermal resistance of a single-finger AlGaN-GaN high electron mobility transistor (HEMT) on three different substrates including Sapphire, SiC and Si. The model reckons the constant thermal conductivity of GaN and substrate, thickness of host substrate layers, gate length (Lg) and width (Wg). The model plausibility is verified by comparing it with DC channel temperature measurement method and charge controlled based device modeling which agrees very favorable observation of the model data. Having nimble expression for the channel temperature is of inordinate importance in the field of designers of power device and monolithic microwave integrated circuits. Proposed model gives a variety of inquiries that would be impossible or impractical to do using time-consuming numerical simulations.

Abstract: We report significant advancements in corona-based non-contact capacitance-voltage (CnCV) metrology recently developed for comprehensive C-V characterization of SiC and other wide bandgap semiconductors. The technique answers the industries needs for nondestructive, cost-effective C-V dopant monitoring for material and device development and manufacturing control. Excellent precision and matching to mercury probe CV is demonstrated for SiC, Ga₂O₃, GaN and AlGaN/GaN structures over a concentration range from 10¹⁴cm^-3 to 2x10¹⁹cm^-3. The emphasis in the present work is on improvement of CnCV in dopant depth profiling resolution and measurement throughout. This is achieved with a variable charge method that in-situ adjusts corona charging increments in response to changes in dopant concentration. Results are presented for multi-layer epitaxial SiC and for 2DEG in AlGaN/GaN HEMT structures. The latter represents an extreme case of high-low concentration profiling with a transition from 10²⁰electrons/cm^-3 in the 2D electron gas to a fully depleted well and dopant concentration in the 10¹⁵cm^-3 range.

Abstract: The n-p-i-n AlGaN solar-blind ultraviolet double heterojunction phototransistor (DHPT) with internal gain is proposed and optimized in this paper. The dependences of spectral responsivity and quantum gain on structure parameters of the AlGaN DHPT are simulated in detail. Then, the polarization effect of AlGaN heterojunction on the performance of AlGaN DHPT is also investigated. Results show that positive polarization charge would enhance the photoresponse of the device, whereas the negative polarization charge would reduce the photoresponse significantly. The reasons for the polarization effect on performance of AlGaN DHPT are discussed.

Abstract: GaN High Electron Mobility Transistors (HEMTs) on SiC have gained remarkable attention as these devices are revolutionizing the power and radio frequency (RF) electronics markets. Although significant advances have been made in transistor technology innovations, innovations pertaining to the backside process technology have been noticeably few. This paper will address and focus on innovations in the backside processing of GaN on SiC devices. A series of innovations in backside processing enable through SiC and GaN via etch rates to exceed 1.5 micron/minute. Wafer dicing process innovations afforded a >4x improvement in sawing throughput and a >6x improvement in blade lifetime through the novel addition of ultrasonic power to a conventional sawing tool.

Abstract: Thin films of gallium nitride (GaN) and related nitride materials were prepared, and their properties as transparent conducting electrodes were investigated. GaN thin films were directly grown on sapphire single crystal substrates by the molecular beam epitaxy. Heavy doping of germanium was employed to reduce resistivity of the films, with sufficient reduction found to be possible while maintaining their epitaxial growth state. Optical transmission spectra of the films in the short wavelength region were slightly deteriorated by the heavy doping; however, this was successfully improved by growing GaN films under metal-rich conditions to increase the electron mobility and suppress unwanted increase of the carrier densities. In addition, the optical transmission spectra in the short wavelength region was improved also by alloying GaN with aluminum nitride, though the resistivities of these films were relatively higher than those of the unmodified GaN films. The prepared nitride thin films exhibited sufficiently suitable properties as transparent conducting electrodes for use in applications such as full-spectrum nitride-based solar cells.

Abstract: We present temperature dependent magnetoresistance measurements on the 2-dimensional electron gas of epitaxially grown AlGaN/GaN heterojunctions on silicon (Si). We report on the quantum correction to the classical conductance. In particular we found weak localization, electron-electron-interaction, and Shubnikov-de Haas oscillations. The results verify the high material quality of the investigated GaN on silicon.

Abstract: The high-Al-content Al_xGa_1-xN alloys, x>0.70, and AlN is the fundamental wide-band-gap material system associated with the technology development of solid-state LEDs operating at the short wavelengths in the deep-UV (λ < 280 nm). Yet, their properties are insufficiently understood. The present study is intended to bring elucidation on the long-time debated and much speculated Si transition from shallow donor in GaN to a localized deep DX defect in Al_xGa_1-xN alloys with increasing Al content. For that purpose electron paramagnetic resonance is performed on a particular selection of high-Al-content epitaxial layers of Al_0.77Ga_0.23N, alternatively Al_0.72Ga_0.28N, alloy composition.

Abstract: The growths of AlN and AlGaN materials were carried out in a home-built metal organic chemical vapor deposition (MOCVD) system. The AlN template was characterized by X-ray diffraction (XRD) and it showed the full width at half magnitude (FWHM) of the x-ray (002) scan rocking curve was only 28 arc seconds, while the FWHM of (102) plane was 252 arc seconds. The results suggested a high quality epitaxial material was obtained. Subsequently, an AlGaN-based violet LED was designed on this template by using AlGaN material as the base. The Al composition of electronic blocking layer (EBL) was optimized. By a quick on-wafer electroluminescence (EL) test, it was demonstrated that the output light intensity of the new structure was at least 15% stronger in comparison to that of the traditional GaN-based violet LED. Finally, fully packaged LEDs were fabricated and the luminous power of the new structure was measured by Spherical integrated system. It was confirmed that a 43% increase of the output power can be obtained.

Abstract: The growth of AlGaN solid solutions on 3C-SiC(111)/Si(111) is demonstrated. The residual stress of the grown layer was investigated by high resolution X-ray diffraction (HRXRD) and infrared ellipsometry. Analysis of the HRXRD data showed that the observed lattice distortion was caused partially by hydrostatic pressure and partially by biaxial tension. The residual stress depends on the layer composition and weakly on the growth temperature.

Abstract: Heteroepitaxial AlGaN/GaN on SiC/Si pseudosubstrate was used to fabricate three-terminal junction devices. Narrow bar and wide bar type active regions were fabricated. The measurement at room temperature showed predicted nonlinear behavior (previously reported about as negative type rectification). Unusual, positive type rectification for two dimensional electron gases was also observed. The electrical characteristics depend on the geometrical configuration of the devices.