III-Nitride is a family of materials including the Nitrides of Gallium (GaN), Indium (InN) and Aluminum (AlN) along with their ternary InGaN, AlGaN, InAlN) and quaternary (InAlGaN) combinations. The ternary and quaternary solid solutions of the III-Nitride family are miscible in the entire composition range, thus tuning the composition of these alloys provides materials with tunable direct band gaps from Near Infrared (0.7 eV, InN) to Deep Ultraviolet (6.2 eV, AlN). Apart from their direct & tunable band gap III-Nitrides also have high absorption coefficient of photons near their band edge (~ 105 cm¬-1), high saturation velocity of electrons (~107cm S-1), high electrical breakdown field (>106 V cm-1) and strong spontaneous and piezoelectric polarization effect. Because of such physical properties, III-Nitride based optoelectronic and high-power, high-frequency electronic devices offer high efficiency, spectral purity, long life time, speed and compactness. However, in the absence of cost effective native substrates, the researchers all over the world must rely on hetero epitaxy methods for fabrication of devices. Some of the popular substrates for heteroepitaxy of III-Nitrides include Silicon, Sapphire and Silicon Carbide. Despite having poor lattice match Silicon has many advantages such as low cost, better electrical conductivity, availability of large wafers which is desired for large scale commercial production and most importantly the cost-effective device fabrication on the platform of Si based integrated circuits. Despite being many decades old, the research on III-Nitrides is yet far from being saturated. Much scope and need is there for inventing newer epitaxial techniques and perfecting the existing ones, to improve the poor crystalline quality of epilayers which results due to lattice and thermal mismatch of the Nitride-epilayer with underlying substrates and there by degrades the device performance. Understanding electrical transport across the III-Nitride heterojunctions and the junctions of III-Nitrides with substrate is another area of research requiring sincere attention both from the fundamental physics and the device point of view. In this talk I will present the effect of different growth parameters during MBE growth of III-Nitrides, on the structural and optical properties of GaN thin films and nanostructures. I will also elucidate my understanding of electrical transport across GaN nano-rods / Si (111) & AlN/Si (111) heterojunctions in the light of temperature dependent current-voltage characteristics. Reference : Journal of Applied Physics 116, 234508 (2014)
Mr. Lokesh Mohan is a PhD candidate at IISc Bengaluru working on III-Nitride materials growth using plasma assisted molecular beam epitaxy (PA-MBE) technique. He has submitted his thesis for his PhD degree. Lokesh has published 10 papers in international journals.