Here, we have demonstrated strong size dependency of quasi-equilibrium and nonequilibrium carrier and photon dynamics in InGaN/GaN single nanowalls using photoluminescence and transient absorption spectroscopy. We demonstrate that two-dimensional carrier confinement, strain relaxation, and modified density of states lead to a reduced Stokes shift, smaller full width at half-maxima, increased exciton binding energy, and reduced nonradiative recombination. The ultrafast transient spectroscopy shows that carrier capture is a two-step process dominated by optical phonons and carrier-carrier scattering in succession. The carrier capture is a strongly size-dependent process and becomes slower due to modulation of the density of available states for progressively decreasing nanowall sizes. The slowest process is the electron-hole recombination, which is also extremely size-dependent and the rate increases by almost an order of magnitude in comparison to that of quantum-well structures. Electron-hole wave function overlap and modified density of states are among the key aspects in determining all the properties of these structures.

We demonstrate a method for nanowire formation by natural selection during wet anisotropic chemical etching in boiling phosphoric acid. Nanowires of sub-10 nm lateral dimensions and lengths of 700 nm or more are naturally formed during the wet etching due to the convergence of the nearby crystallographic hexagonal etch pits. These nanowires are site controlled when formed in augmentation with dry etching. Temperature and power dependent photoluminescence characterizations confirm excitonic transitions up to room temperature. The exciton confinement is enhanced by using two-dimensional confinement whereby enforcing greater overlap of the electron-hole wave-functions. The surviving nanowires have less defects and a small temperature variation of the output electroluminescent light. We have observed superluminescent behaviour of the light emitting diodes formed on these nanowires. There is no observable efficiency roll off for current densities up to 400 A/cm2.

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We have demonstrated an electrically injected ultra-low threshold (8.9 nA) room temperature InGaN/GaN based lateral nanowire laser. The nanowires are triangular in shape and survived naturally after etching using boiling phosphoric acid. A polymethyl methacrylate (PMMA) and air dielectric distributed mirror provide an optical feedback, which together with one-dimensional density of states cause ultra-low threshold lasing. Finite difference eigen-mode (FDE) simulation shows that triangular nanowire cavity supports single dominant mode similar to TE01 that of a corresponding rectangular cavity with a confinement factor of 0.18.

The effect of polarization modulation on GaN-based double-barrier resonant tunneling diodes is theoretically investigated. The polarization field is shown to improve the performance of these devices by increasing the peak current, peak-to-valley ratio, and negative differential conductance. The high sensitivity of the quantum-well bound energy state with the applied bias explains the observed characteristics. We have further demonstrated that a thin In0.1Ga0.9N layer can significantly improve the performance of the devices by introducing an additional polarization field beyond the second barrier, which reduces the device series resistance and increases the effective second barrier height and width.

III-V compound semiconductors laid the foundation for optoelectronic devices and solid-state lighting with wavelengths ranging from infrared to ultraviolet regions. Infrared to green light-emitting diodes (LEDs) were invented in the early 1960s. [1][2][3] However, blue LEDs took another three decades to get established, considering the challenges in defect-free high-quality growth, [4][5][6] and controlled p-doping of wide-bandgap semiconductors. [7][8][9][10] The success of blue LEDs was accomplished by the development of gallium-nitride (GaN) alloyed with indium and aluminum in the late 1980s. [11,12] GaN and related materials have a wurtzite crystal structure and direct bandgap, making them ideal for bright LEDs and laser diodes (LDs). In order to move the emission wavelength to the visible range (2-3.4 eV), InN is alloyed with GaN. [13,14] Advancement in GaN-based LEDs revolutionized the white broadband lighting when laminated with yellow phosphorous coating. Nakamura et al. developed the first high-quality InGaN back in 1992, which paved the way for III-nitride blue and green LEDs/ LDs. [15] In 1995-1996, Nakamura made true blue LEDs possible by developing recombination regions with InGaN. [16] III-nitride devices acquire a wide area of applications due to their wavelength tunability by varying the alloy composition of In and Al in InGaN and AlGaN, respectively. [17,18] Moreover, an additional degree of freedom can be achieved using quantum-confined nanostructures. Emission wavelength and surface/interface material properties can be altered by reducing the dimensionality/size of the devices. [19][20][21] quantum well (QW; 2D), [22][23][24] vertical/lateral nanowires (1D), [25][26][27][28][29] and quantum dots (QDs; 0D) [30][31][32][33] are among the most important quantum-confined nanostructures used in the active regions of modern optoelectronic devices including LEDs, lasers, photodetectors, and solar cells. Improved internal quantum efficiency, [34][35][36] large surface-to-volume ratio, [37] low power

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GaN based nanostructures are being increasingly used to improve the performance of various devices including light emitting diodes and lasers. It is important to determine the strain relaxation in these structures for device design and better prediction of device characteristics and performance. We have determined the strain relaxation in InGaN/GaN nanowalls from quantum confinement and exciton binding energy dependent photoluminescence peak. We have further determined the strain relaxation as a function of nanowall dimension. With a decrease in nanowall dimension, the lateral quantum confinement and exciton binding energy increase and the InGaN layer becomes partially strain relaxed which decreases the piezoelectric polarization field. The reduced polarization field decreases quantum confined Stark effect along the c-axis and increases electron-hole wave-function overlap which further increases the exciton binding energy. The strong dependency of the exciton binding energy on strain is used to determine the strain relaxation in these nanostructures. An analytical model based on fractional dimension for GaN/InGaN/GaN heterostructures along with self-consistent simulation of Schrodinger and Poisson equations are used to theoretically correlate them. The larger effective mass of GaN along with smaller perturbation allows the fractional dimensional model to accurately describe our system without requiring first principle calculations.