Papers by Keyword: AlGaN/GaN HEMT

Abstract: Higher frequency hetero-junction transistors called High Electron Mobility Transistors (HEMTs) are employed in a number of high-power applications, including radiofrequency, radiation, space exploration, and others. When stressed between the junction of a broad bandgap and low bandgap material, AlGaN/GaN HEMTs create Two-Dimensional Electron Gas (2DEG).To determine the eventual number of electrons in the quantum well, it is necessary to assess the charge density generated by the polarization existing in the 2DEG region. In this paper, two-dimensional electron gas (2-DEG) sheet carrier concentration estimate model takes into consideration the substantially dominating total polarization. In order to regulate the impact of these characteristics on the device performance, discussion has focused on the current-voltage characteristic, which illustrates how the drain-source current varies in response to the gate voltage modulation. Our study also aims at how the two-dimensional electron gas density depends on the aluminum molar percentage and AlGaN layer thickness.

Abstract: In this study, the results indicate that a method combining fully-recessed wet etching and regrown channel by MOCVD is capable of obtaining high quality interface in GaN MIS-HEMT. A low V_th hysterisis GaN MIS-HEMT of 0.3V is demonstrated in this work. The GaN MIS-HEMT has a V_th of-1.5 V, a high I_d,max of 771mA/mm and a R_ON of 13.5 Ω·mm. The wet etching shows good uniformity while the MOCVD grown AlN enhances the maximum drain current. The concept provides new insights to gate recess fabrication and MOCVD grown high quality dielectrics.

Abstract: In the process of characterizing AlGaN/GaN HEMTs on Si (111), Sapphire, 4H-SiC substrates, various Rapid Thermal Annealing (RTA) conditions for the Ti/Al/Ta/Au ohmic contact process and the resulting surface analysis have been investigated. In order to achieve a low ohmic contact resistance (RC) and a high quality surface morphology, we tested seven steps (800 °C to 920 °C) annealing temperatures and two steps (15, 30 sec) annealing times. According to these annealing temperatures and times, the optimal ohmic resistance of 3.62 × 10^-6 Ohm • cm² on Si(111) substrate, 9.44 × 10^-6 Ohm • cm² on Sapphire substrate and 1.24 × 10^-6 Ohm • cm² on 4H-SiC substrate are obtained at an annealing temperature of 850 °C and an annealing time of 30 sec, 800 °C and an annealing time of 30 sec and 900 °C and an annealing time of 30 sec, respectively. The surface morphologies of the ohmic contact metallization at different annealing temperatures are measured using an Atomic Force Microscope (AFM). AFM morphology Root Mean Square (RMS) level determines the relationship of the annealing temperature and the annealing time for all of the samples. According to these annealing temperatures and times, the optimal ohmic surface RMS roughness of 13.4 nm on Si(111) substrate, 3.8 nm on Sapphire substrate and 2.9 nm on 4H-SiC substrate are obtained at an annealing temperature of 850 °C and an annealing time of 30 sec, 800 °C and an annealing time of 30 sec and 900 °C and an annealing time of 30 sec, respectively.

Abstract: AlGaN/GaN high electron mobility transistors (HEMTs) have shown outstanding improvements in performance and reliability, becoming the leading option for power applications in the 1-40 GHz range. However, the presence of traps and defects in the hetero-structure are strongly correlated to the tolerance of the fabrication process. New powerful models designed to overcome limitations associated with the Process Variability (PV) may be part of the exploitation outcome. This work describes a methodology useful to characterize the effects of PV on AlGaN/GaN HEMTs performance, by deriving Process Compact Model (PCM) from systematic TCAD simulations. The device under examination is an Al_0.26Ga_0.74N/GaN HEMT and the selected critical process parameters are: molar fraction of the first AlGaN layer, AlGaN layer thickness, source-gate and drain-gate distance, field plate extension, gate height and width, recessed effect under the gate contact.

Abstract: AlGaN/GaN high electron mobility transistors (HEMTs) were grown on un-patterned, patterned without mask, and patterned with mask Si (111) substrates by metal organic chemical vapor deposition (MOCVD). The patterns on the Si substrates were fabricated by SiO2 masks and wet etching. Double AlN interlayers grown at high temperature were employed to relax the tensile stress induced by the large mismatches in the lattice constants and the thermal expansion coefficients. Growth characteristics of AlGaN/GaN HEMTs were discussed and analyzed. Before achieving optimized growth conditions, more cracking lines were observed on patterns along the [1-100] orientation than along the [11-20] orientation, resulted from more stable GaN (1-100) facets than GaN (11-20) facets. It is suggested that long patterns should be made along the [11-20] orientation. Micro-Raman measurements showed that Raman shifts at the concave corners are bigger than those at the convex corners, indicating the presence of the larger stress at the concave corners.

Abstract: We investigated the current collapse characteristics of the fabricated MIS-HEMT with the SiO2, SiN and high-k gate insulator. TiO2 was employed as the high-k material. We found the significant drain current change in the switching characteristic when the insulator changes. The SiN MIS-HEMT showed good switching characteristic. On the other hand, the MIS-HEMTs with oxide insulator film showed large drain current reduction. We considered that the degradation of the switching characteristic is due to the current collapse.

Abstract: Confocal μ-Raman was used to measure the operating temperatures in SiC MESFETS, AlGaN/GaN/SiC HEMT’s and 4H-SiC PiN diodes. Temperatures obtained from thermal imaging of the MESFETS compared well with those measured from Raman scattering. Operating temperatures were also obtained for large area PiN diode and it was shown that a single point at the center of the device can be used to measure the average temperature.

Abstract: The mechanism of drain current collapse in AlGaN/GaN high electron mobility transistors (HEMTs) was investigated. Current collapse was clearly observed for TiO2 passivated HEMTs. However, no evidence of current collapse was apparent for SiNx passivated HEMTs. This suggests that AlGaN surface traps play a major role in current collapse. The experimental results were compared with numerical device simulation results. The device simulations were performed taking into account hot electron generation and deep traps at the AlGaN surface. The simulated drain current transients were consistent with the degradation and recovery behavior of the experimental results. These results indicate that current collapse is caused by the trapping of hot electrons in deep levels at the AlGaN surface.