Abstract
We investigate the electrical characteristics of Schottky contacts for an Au/hydride vapor phase epitaxy (HVPE) a-plane GaN template grown via in situ GaN nanodot formation. Although the Schottky diodes present excellent rectifying characteristics, their Schottky barrier height and ideality factor are highly dependent upon temperature variation. The relationship between the barrier height, ideality factor, and conventional Richardson plot reveals that the Schottky diodes exhibit an inhomogeneous barrier height, attributed to the interface states between the metal and a-plane GaN film and to point defects within the a-plane GaN layers grown via in situ nanodot formation. Also, we confirm that the current transport mechanism of HVPE a-plane GaN Schottky diodes grown via in situ nanodot formation prefers a thermionic field emission model rather than a thermionic emission (TE) one, implying that Poole–Frenkel emission dominates the conduction mechanism over the entire range of measured temperatures. The deep-level transient spectroscopy (DLTS) results prove the presence of noninteracting point-defect-assisted tunneling, which plays an important role in the transport mechanism. These electrical characteristics indicate that this method possesses a great throughput advantage for various applications, compared with Schottky contact to a-plane GaN grown using other methods. We expect that HVPE a-plane GaN Schottky diodes supported by in situ nanodot formation will open further opportunities for the development of nonpolar GaN-based high-performance devices.
Highlights
Polarization-free nonpolar a-plane GaN layers have been extensively considered as an adequate material for high-performance GaN-based optoelectronic devices owing to the absence of the quantum-confined Stark effect (QCSE) along its orientation [1,2]
I–V–T measurements, conduction models, and deep-level transient spectroscopy (DLTS) analysis have been employed to investigate the electrical characteristics of Schottky diodes fabricated on hydride vapor phase epitaxy (HVPE) a-plane GaN templates grown using in situ GaN nanodot formation
Deviated ideality factors from unity reveal the inhomogeneity of the barrier height, which was confirmed by conventional Richardson, barrier height, and ideality plots
Summary
Polarization-free nonpolar a-plane GaN layers have been extensively considered as an adequate material for high-performance GaN-based optoelectronic devices owing to the absence of the quantum-confined Stark effect (QCSE) along its orientation [1,2]. Due to the lack of native bulk GaN, researchers have been investigating the growth of a-plane GaN with improved structural properties grown on foreign substrates, using metal organic vapor phase epitaxy (MOCVD), molecular beam epitaxy (MBE), or hydride vapor phase epitaxy (HVPE) [7,8,9,10] Among these methods, HVPE nonpolar a-plane GaN templates have attracted considerable attention for their high throughput and relatively good crystal quality, and in view of their efficient and effective commercial advantages [11,12]. We proposed the simple and efficient method of growing HVPE thick GaN layers using in situ formation of GaN nanodots without any external processes [16] This can be applied to any Al2O3 substrate regardless of crystal orientation, the electrical properties of contacts between the metal and a-plane GaN template have to be explored for their opto-electrical applications such as light-emitting diodes (LEDs), laser diodes (LDs), and power electronics. Even though some works have reported the barrier and current characteristics between the a-plane GaN and metal contact [17,18], none have investigated the Schottky mechanism of metal and HVPE a-plane GaN templates grown via in situ GaN nanodot formation
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