We report the Frenkel-Poole emission in Pt/Au Schottky contact on Ga-polarity GaN grown by molecular beam epitaxy using current-voltage-temperature (I-V-T) characteristics in the temperature ranging from 200 K to 375 K. Using thermionic emission model, the estimated Schottky barrier height is 0.49 eV at 200 K and 0.83 eV at 375 K, respectively, and it is observed that the barrier height increases with increase in temperature. The extracted emission barrier height (ϕt) for Ga-polarity GaN Schottky diode by Frenkel-Poole theory is about 0.15 eV. Deep level transient spectroscopy study shows a deep level with activation energy of 0.44 eV, having capture cross-section 6.09 × 10−14 cm2, which is located between the metal and semiconductor interface, and trap nature is most probably associated with dislocations in Ga-polarity GaN. The analysis of I-V-T characteristics represents that the leakage current is due to effects of electrical field and temperature on the emission of electron from a trap state near the metal-semiconductor interface into continuum states associated with conductive dislocations in Ga-polarity GaN Schottky diode.
It is found that the surface migration and nucleation behaviors of InSb quantum dots on AlSb/Si substrates, formed by molecular beam epitaxy in Stranski-Krastanov (SK) growth mode, are dependent on the substrate temperature. At relatively high temperatures above 430 degrees C, quantum dots are migrated and preferentially assembled onto the surface steps of high defect AlSb layers grown on Si substrates, while they are uniformly distributed on the surface at lower temperatures below 400 degrees C. It is also found that quantum dots located on the defect sites lead to effective termination of the propagation of micro-twin-induced structural defects into overlying layers, resulting in the low defect material grown on a largely mismatched substrate. The resulting 1.0 microm thick Al(x)Ga(1-x)Sb (x = 0.8) layer grown on the silicon substrate shows atomically flat (0.2 nm AFM mean roughness) surface and high crystal quality, represented by a narrow full width at half-maximum of 300 arc s in the x-ray rocking curve. The room-temperature electron mobility of higher than 16 000 cm(2) V(-1) s(-1) in InAs/AlGaSb FETs on the Si substrate is obtained with a relatively thin buffer layer, when a low defect density ( approximately 10(6) cm(-2)) AlGaSb buffer layer is obtained by the proposed method.
The microstructural properties of a GaN layer grown on a patterned sapphire substrate (PSS) were studied in detail using transmission electron microscope techniques to determine dislocation and growth behaviors. Regular and uniform recrystallized GaN islands were observed on the protruding pattern. On a flat sapphire surface, the crystallographic orientation relationship of ⟨1¯21¯0⟩GaN on FS//⟨11¯00⟩sapphire and {11¯01}GaN on FS//{12¯13}sapphire existed between the GaN and the substrate. On the other hand, the orientation relationship of ⟨1¯21¯0⟩GaN layer//⟨1¯21¯0⟩GaN island on IS//⟨11¯00⟩sapphire and {11¯01}GaN layer//{0002}GaN island on IS//{12¯13}sapphire was confirmed among the GaN layer, the recrystallized GaN islands on an inclined sapphire surface and the PSS. The flat surface among the protruding patterns began to fill rapidly with GaN. Then, the GaN gradually overgrew the protruding pattern and coalesced near the summit as the growth time increased. The generation of threading dislocations was observed in the vicinity of the coalescence points near the top of the protruding patterns.
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