Polarization-doping via graded AlGaN layer on N-face (0001¯) GaN has been demonstrated as an inspiring p-type doping method for wide-band-gap nitrides. However, the polarity of III-nitrides grown by metal organic chemical vapor deposition is metal-face typically. In this paper, we show that three-dimensional mobile hole gas induced by polarization can be formed in (0001)-oriented metal-face III-nitride structure. The hole concentration of a Mg-doped AlxGa1−xN layer with graded Al composition from x=0.3 to 0 grown on AlN buffer layer is remarkably enhanced, compared with that of a Mg-doped GaN layer grown under the same conditions. In addition, the hole concentration in the graded AlGaN layer is absence of freezeout as the temperature decreases, indicating that the hole is induced by polarization. This p-type doping method paves a way for achieving high-efficiency in wide-band-gap semiconductor light-emitting devices with p-type doping problem.
Insufficient hole injection is a major impediment to the luminescence efficiency of III-nitride light-emitting diodes (LEDs). In our previous work by Zhang et al. [Appl. Phys. Lett. 97, 062103 (2010)], high-density mobile three-dimensional hole gas is obtained in Mg-doped Al composition graded AlGaN layer with Al composition linearly decreasing from a certain value to 0. In this paper, it is revealed by a theoretical study that the hole injection efficiency in blue-light GaN-based LEDs can be greatly enhanced by using this polarization-doped method. An increase in the electroluminescence intensity and the internal quantum efficiency in polarization-doped GaN-based LEDs is observed, in comparison with a conventional LED.
To integrate plasmonic devices into industry, it is essential to develop scalable and CMOS compatible plasmonic materials. In this work, we report high plasmonic quality titanium nitride (TiN) on c-plane sapphire by plasma enhanced atomic layer deposition (PE-ALD). TiN with low losses and high metallicity was achieved at temperatures below 500°C, by exploring the effects of chemisorption time, substrate temperature and plasma exposure time on material properties. Reduction in chemisorption time mitigates premature precursor decomposition at TS > 375°C , and a trade-off between reduced impurity concentration and structural degradation caused by plasma bombardment is achieved for 25s plasma exposure. 85 nm thick TiN films grown at a substrate temperature of 450°C, compatible with CMOS processes, with 0.5s chemisorption time and 25s plasma exposure exhibited a high plasmonic figure of merit (| ′ / ′′ |) of 2.8 and resistivity of 31 μΩ − cm. These TiN thin films fabricated with subwavelength apertures were shown to exhibit extraordinary transmission.
This article provides an overview of recent development of sputtering method for high-quality III-nitride semiconductor materials and devices. Being a mature deposition technique widely employed in semiconductor industry, sputtering offers many advantages such as low cost, relatively simple equipment, non-toxic raw materials, low process temperatures, high deposition rates, sharp interfaces, and possibility of deposition on large-size substrates, including amorphous and flexible varieties. This review covers two major research directions: (1) ex situ sputtered AlN buffers to be used for subsequent growth of GaN-based structures by conventional techniques, such as metal-organic chemical vapor deposition (MOCVD), hydride vapor phase epitaxy (HVPE), or molecular beam epitaxy (MBE), and (2) deposition of the entire III-nitride layered stacks and device structures by sputtering. Replacing conventional in situ GaN or AlN buffer layers with ex situ sputtered AlN buffers for MOCVD, HVPE, or MBE growth of IIInitride films on sapphire and silicon substrates results in the improved crystal quality through reduction in dislocation density and residual strain. Extensive efforts in the field of sputter deposition of III-nitrides resulted in crystalline quality of sputtered III-nitride films compatible with that of MOCVD and MBE grown layers despite the lower temperatures used in sputtering. For example, sputtering techniques made it possible to achieve GaN layers heavily doped with Si and Ge to electron concentrations in mid-10 20 cm −3 range with mobilities exceeding 100 cm 2 V −1 s −1 , resulting in conductivities as high as those of benchmark transparent conducting oxides such as indium tin oxide (ITO). For moderate levels of doping with Si, mobilities comparable to state-of-the-art MOCVD-grown material have been demonstrated (up to ∼1000 cm 2 V −1 s −1 ). The first promising results have been reported for devices (light emitters and field effect transistors) entirely produced by sputtering.
By coupling photons into collective oscillations of free electrons, plasmonics enables the emergence of novel technologies with the combined capabilities of photonics and miniaturized electronics. [1] In the past few decades, a large variety of plasmonicsbased applications have been demonstrated. These include nanolasers, [2,3] interconnects, [4,5] modulators, [5][6][7][8][9] chemicaland bio-sensors, [10,11] as well as light-emitting diodes and photovoltaic devices where plasmonics is used for efficiency enhancement. [12,13] One of the most attractive materials alternative to noble metals that drive the plasmonics revolution, is titanium nitride (TiN), which has been investigated extensively due to its low-cost, gold-like, and tunable optical properties in the visible and near-infrared range, high thermal and chemical stability, high mechanical hardness, and bio-and complementary metaloxide-semiconductor (CMOS) compatibilities. [14] TiN has been widely used as a gate electrode in various CMOS devices. [15][16][17][18] In the area of plasmonics, TiN-based waveguides, [19] gyroidal metamaterials, [20] nanohole metasurfaces, [21] nanoantennas, [22][23][24] and use of TiN nanoparticles for solar energy conversion [25,26] and biomedicine [27] have been reported.However, the majority of the demonstrations of TiN's device potential in plasmonics have been on sapphire and bulk MgO substrates featured by their small lattice mismatch with TiN, enabling the best-performing plasmonic films. [24,[28][29][30][31][32][33] Even then, high deposition temperatures (not congruent with CMOS processes) were usually used to ensure the high structural quality of the TiN films. For example, using reactive sputtering and at a substrate temperature of 650 C, a peak plasmonic figure of merit (FOM ¼ Àε 0 /ε 00 ) of %4.5 has been demonstrated for TiN films on a bulk MgO substrate. [24] Single-crystalline, highly metallic TiN films with an electron concentration of 9.2 Â 10 22 cm À3 and a peak plasmonic FOM as high as %5.8 have been achieved on c-sapphire substrates by plasma-assisted molecularbeam epitaxy (PA-MBE) at a substrate temperature of 1000 C. [28] However, realizing the true potential of TiN-based plasmonics through integration with the CMOS electronics necessitates
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