Papers by Keyword: AlGaN/GaN

Abstract: Metal organic chemical vapor deposition (MOCVD) was used to grow AlGaN/GaN HEMT on a sapphire substrate with a 3.0 nm GaN cap and a sample without a GaN cap. High resolution X-ray diffraction (HRXRD) was utilized to investigate the structural characteristics of the materials. The relationship between the electrical properties and two-dimensional electron gas (2DEG) I-V and Hall Effect measurement. The I-V measurement was used to investigate the resistance properties of AlGaN/GaN heterostructures. Hall Effect measurement was used to quantify electron mobility and sheet carrier concentration in both samples. The sample with a 3.0 nm GaN cap exhibited excellent electrical properties with 436.8 Ω/sq sheet resistivity and possessed a high value of sheet carrier concentration 3.46E+14 per cm².

Abstract: Different material thickness with medium and high dielectric constant can impact the performance and reliability of high electron mobility transistor device. With varying the thickness of the passivation layer, the effect of it towards the device performance is still unclear. Two different insulator layers with a medium dielectric and a high dielectric constant namely Aluminium Nitride and Hafnium Oxide are used as passivation layer in AlGaN/GaN HEMT. Both material performance was simulated via COMSOL software by varying the thickness and the drain current output were compared. The passivation layer thickness of 10nm at V_ds=6 V and V_gs=5 V, HfO₂ outperforms AlN with the output drain current of 39 mA compared to 35 mA respectively. It was observed that HfO₂ can attain higher threshold voltage, V_th as compared to the AlN because of the influence of its material properties that shows a direct proportional relationship between V_th and dielectric constant. Using high dielectric constant material like HfO₂, we observe the ON-voltage gradually decreases as the thickness of the passivation layer increased. Out of all the thickness simulated for HfO₂ and AlN, 10nm produced the highest drain current output instead of layer thickness of 20nm.

Abstract: AlGaN/GaN heterostructure was observed using scanning nonlinear dielectric microscopy, which can measure both carrier and polarization profile in AlGaN/GaN heterostructure. As a result, GaN spontaneous polarization and AlGaN polarization which was sum of spontaneous polarization and piezoelectric polarization were clearly distinguished. Moreover, two dimensional electron gas was observed at the AlGaN/GaN interface. These results show that scanning nonlinear dielectric microscopy is useful method for evaluation of two dimensional electron gas profile and polarization profile in AlGaN/GaN heterostructure.

Abstract: In this work, the different nature of trapping states in metal-oxide-semiconductor (MOS) capacitors fabricated on recessed AlGaN/GaN heterostructures has been investigated. In particular, the origin of both fast and slow states has been elucidated by frequency dependent conductance measurements. Using post deposition annealing in forming gas, which is known to induce hydrogen incorporation at the interface, allowed to ascribe the fast traps (with characteristic response time in the range of 5–50 μs) to SiO₂/GaN interface states and the slow traps (50–100 μs) to “border traps” located few nanometers inside the SiO₂ layer. The results can be useful to predict the behavior of GaN switching devices, like hybrid MOSHEMTs.

Abstract: Metal-insulator-semiconductor (MIS) diodes with Si₃N₄/Al₂O₃ bilayer gate dielectric films deposited on an AlGaN/GaN heterostructure were fabricated, where the Si₃N₄ layer played a role of etching stopped layer to protect the Al₂O₃ film from being damaged. Compared with traditional Schottky diodes, a distinct suppression of gate leakage current was achieved for the MIS diodes both at forward and reverse bias, and the dominant leakage current mechanism is Fowler–Nordheim tunneling. The 2DEG density extracted from C-V curves was 3~7 ́10¹³cm^-2, in the same order of magnitude as Schottky diodes and hall measurement. Although the existence of the bilayer dielectric did not affect the 2DEG density at the interface of AlGaN/GaN, Si₃N₄ layer shared more gate bias and led to more gate bias required to deplete 2DEG and turn down the devices, moreover, Si₃N₄ layer had no effect on suppressing the forward or reverse gate leakage current due to its narrow band gap width and band bending compared with a single Al₂O₃ film. The experimental results provided a reference for the design of gate dielectric film structure for AlGaN/GaN high-electron-mobility transistors (HEMTs).

Abstract: Magnetotransport properties are investigated in two-dimensional electron gas (2DEG) of AlGaN/GaN heterostructure, including the Drude conductance, the Shubnikov-de Haas (SdH) oscillations and the change with temperature, the electron-electron interaction (EEI) and the change with temperature, the weak antilocalization (WAL) and the change with temperature etc.

Abstract: The effects of low energy (1.8 MeV) electron irradiation on enhancement-mode (E-mode) AlGaN/GaN high electron mobility transistors (HEMTs) have been reported. When the dose up to 1.1×10¹⁶ cm^-2, the saturation drain current and maximal transconductance of E-mode AlGaN/GaN HEMTs increase after irradiation. However, almost no change of threshold voltage and gate leakage current is observed. The results are explained by the creation of positive charges in the AlGaN layer by ionizing energy loss, especially the creation of N vacancies and Ga vacancies by non-ionizing energy loss. Moreover, low-energy electron irradiation could recover the electron mobility.

Abstract: The impact of the thickness of an AlN spacer in AlGaN/AlN/GaN high electron mobility transistor (HEMT) structures on the Hall mobility was investigated in a range of 30 K - 340 K. The AlN spacer has a strong impact on the mobility at temperatures below 150 K. This effect is linked to a reduction of alloy scattering. Optical and scanning electron microscopy revealed hexagonal shaped defects which also have an effect on the mobility. These defects can be avoided by an appropriate adjustment of the AlN layer thickness.

Abstract: The electrical properties of AlGaN/GaN heterojunction high electron mobility transistor (HEMT) are simulated by using sentaurus software. This paper compares two structures, the HEMT with GaN cap layer and the HEMT without GaN cap layer. The sentaurus software simulates the DC and AC characteristics of the two AlGaN/GaN HEMT structures. The HEMT with GaN cap layer can increase the maximum transconductance g_m from 177ms/mm to 399ms/mm when the doping concentration of the cap layer is 3×10¹⁸cm^-3 compared with the other structure under the same conditions. The simulation results indicate that the HEMT with cap layer can increase maximum transconductance g_m, saturation current I_ds, current-gain cutoff frequency f_T, maximum oscillation frequency f_max and reduce the series resistance of the drain to source compared with the HEMT without GaN cap layer. The large I_ds of the HEMT with cap layer is attributed to the increase of the concentration of two dimensional electron gas (2DEG). Moreover, the change of the doping concentration of the cap layer will affect the g_m and I_ds.

Abstract: Al-Free Nanolayered Metallizations Based on the Transition Metals Ti, Mo, Ni and Pd, with Varied Ti Content, Have Been Developed as an Alternative of the Al-Based Contacts for Sub-Micron Hemts. the Electrical, Morphological and Thermal Properties of the Metallization Schemes Have Been Studied with the Aim of Obtaining the Most Suitable Combination of Low Resistivity, a Smooth Surface and an Acute Edge. the Lowest Resistivity of 8.8x 10-6 Ω.cm2 Has Been Determined with the Ti/Mo/Ti/Au Contact, while the Lowest Surface Roughness of 6 Nm Has Been Measured for the Ti/Ni/Ti/Au Metallization. these Contact Schemes Have Shown much Better Edge Acuity in Comparison to the Al-Based Metallizations.