Yüksek Güç Uygulamaları İçin Galyum Nitrür Temelli Yüksek Elektron Hareketlilikli Transistör Tasarımı, Fabrikasyonu ve Karakterizasyonu
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In this study, novel epitaxial structures for high power applications have been grown by using Metal-Organic Chemical Vapour Deposition (MOCVD) technique. Photoluminescence (PL), Atomic Force Microscopy (AFM), X-Ray Diffraction (XRD), Hall Effect Measurement Systems, Differential Interference Contrast (DIC) Microscopy and Mechanical Profilometer were used for electrical and structural analysis of the grown epitaxial samples. High electron mobility transistor (HEMT) device fabrication was performed on these epitaxial samples. DC I-V and RF (Radio Frequency) power characterization were carried out and the most suitable structure was determined by experimental methods for high power applications. Device structure simulation studies were performed on the determined epitaxial structure for high power HEMT devices operating in the X-band range (8-12 GHz) by using the Silvaco ATLAS program. In the simulation studies when the gate length 〖(L〗_G) is 300 nm, It was seen that as the gate-source distance 〖(L〗_GS) increases, the maximum saturation current 〖(I〗_DSS), the transconductance 〖(g〗_m) and the maximum DC output power 〖(P〗_(DC_max)) decrease and I_DSS, g_m and breakdown voltage 〖(V〗_br) do not change much as the distance between drain and source 〖(L〗_DS) increases. As a result of the simulation studies, optimum values for L_G, L_GS ve L_DS were determined as 300 nm, 800 nm and 3 μm respectively. HEMT devices with an I-gate with a Field Plate, a Standing Gamma (Γ)-Gate on Si3N4 and a Gamma (Γ)-Gate, Partially Embedded in Si3N4 and Partially Standing in the Air were simulated by using these values. HEMT device fabrication was performed for gate types such as I-gate (Type-1), I-gate with a field plate (Type-2), a Standing Gamma (Γ)-Gate on Si3N4 (Type-3), Recessed Gamma (Γ)-Gate (Type-4), a Gamma (Γ)-Gate, Partially Embedded in Si3N4 and Partially Standing in the Air (Type-5) by using the optimized simulation results. The maximum saturation current 〖(I〗_DSS), transconductance 〖(g〗_m), pinch-off voltage 〖(V〗_th), current-gain cutoff frequency 〖(f〗_T), maximum oscillation frequency 〖(f〗_max) and RF characteristics of the devices in terms of the small-signal gain and RF output power 〖(P〗_out) at 8 GHz were investigated. The results showed that the output power is increased 1 dB when the gate structure changed from field plate to gamma gate. The V_th, g_m, f_T and f_max values are maximized when the thickness of the passivation layer between the gate foot and the gate head is minimized. I_DSS is decreased and P_out is increased, respectively, when the gate recess etching process is performed.