uan Li

Influence of the Aln/Gan superlattices buffer thickness on the electrical properties of Algan/Gan HFET on Si substrate

The influence of the total thickness (periods of AlN/GaN SLs) of AlN/GaN superlattices (SLs) buffer on the static electrical properties of AlGaN/GaN HFETs is study for the purpose of improving devices breakdown voltage (BV) and reducing its on-resistance (R<inf>ON</inf>). It is found that for top-GaN layer with a constant thickness of lμm, a proper thickness of AlN/GaN SLs buffer (such as 2.5 μm with 100 period AlN/GaN SLs) could obtain better crystal quality of top-GaN layer as well as more robust devices with more superior performance in all aspects. The most robust HFETs in this work have achieved a specific on-resistance (R<inf>ON, SP</inf>) of 0.68 mΩ-cm² (@ L<inf>GD</inf>=4μm), a maximum on-state drain current (I<inf>D, max</inf>) of 430 mA/mm (@ L<inf>GD</inf>=4μm), an On/Off ratio of 2×10⁸, a BV of 552V at a drain leakage current of lμA/mm (@ L<inf>GD</inf>=15μm), and a figure-of-merit (FOM=BV²/R<inf>ON, SP</inf>) of 168 MW/cm² (@ L<inf>GD</inf>=8μm).

Influence of AlGaN back barrier layer thickness on the dynamic ron characteristics of AlGaN/GaN HEMTs

AlGaN back barrier with different thickness is used in AlGaN/GaN high electron mobility transistors (HEMTs) to evaluate the device performances. It shows that a proper AlGaN back barrier thickness (tbb ∼100 nm) is beneficial for obtaining low leakage current and high Ion/Ioff ratio of approximately 108. While further increasing the AlGaN thickness can deteriorate the device performances because of the generation of more surface defects. The dynamic on-resistance (RON) degradation measurements demonstrate that the proper AlGaN back barrier thickness (tbb) can not only improve the 2DEG confinement, but also prevent electrons penetrating into buffer layer. Thus, it results in the reduction of trapping effect and then the improvement of dynamic RON.

A novel normally-off GaN MISFET with an in-situ AlN space layer using selective area growth

In this paper, we present a recessed-gate normally-off Al₂O₃/AlN/GaN MISFET with stable threshold voltage based on selective area growth (SAG) of AlGaN/GaN heterostructure on AlN/GaN/Si template. By in-situ growth of a thin AlN space layer (SL) in MOCVD, GaO_x can be blocked fundamentally and a high-quality Al₂O₃/AlN/GaN interface is achieved. Thus, the device exhibits a comprehensive upgrade performance with a low threshold voltage hysteresis (ΔV_th) of 75 mV at V_g=10 V, a high peak field-effect mobility (μ_FE) of 187 cm²/V-s, a maximum drain current of 620 mA/mm and an improved frequency dispersion.

Effect of Gan interlayer thickness on the Algan/Gan heterostructure field-effect transistors for self-terminated wet etching process

In this paper, we investigated the effect of GaN interlayer thickness and AlGaN back barrier layer on the material and electrical properties of AlGaN/GaN HFETs. When the thickness of GaN interlayer is approximately 3 and 5 nm, it will slightly increase surface roughness and degrades 2DEG carrier density. The 2DEG channel is also up shifted to nearly beneath the GaN interlayer. By contrast, 10 nm GaN interlayer causes a clear double channel and an obvious degradation of 2DEG carrier density. It is also demonstrated that the introduction of AlGaN back barrier layer can effectively improve the 2DEG confinement and reduce the scattering, resulting in smaller frequency dispersion effect. HFETs fabricated on the sample with both back barrier layer and 5 nm GaN interlayer present good pinch-off characteristics and high on/off ratio of approximately 107. This optimized structure is suitable for application in self-terminated wet etching process.

The breakdown behavior of GaN epitaxial material on silicon

In this paper, the leakage path and breakdown behavior of GaN on silicon substrate were studied systematically. Three terminal breakdown voltage characteristics of the samples with various ohmic contacts spacing were evaluated. With increasing the spacing between the contacts, the breakdown voltage increased linearly first and then saturated. In order to clarify the breakdown behavior, leakage path after breakdown test was further analyzed and the breakdown behaviors were identified. Furthermore, the burnt buffer layer was observed by FIB SEM after device breakdown intuitively. It manifested that the spacing dependent breakdown characteristics of the epitaxial layer was ascribe to that different leakage paths dominated the breakdown at different spacing.