Structural and electrical characterization of GaN based hetero-structures

• Main Author: Agarwal, Ananya
• Other Authors: K Radhakrishnan
• Format: Final Year Project
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Electrical and electronic engineering
• Online Access: http://hdl.handle.net/10356/53109
• Institution: Nanyang Technological University

The thesis discusses about the structural and electrical properties of GaN based materials. The literature review covers basic concepts of GaN materials and high electron mobility transistors (HEMTs). In particular, detailed explanation on the polarization charges that are present in AlGaN/GaN HEMT structures and the formation of two dimensional electron gas has been discussed. Molecular beam epitaxy technique and its applicability for growing nitride based semiconductors are also presented. Furthermore, the structural and electrical characterization techniques are discussed in detail. These techniques include Atomic Force Microscopy (AFM) to characterize the surface morphology and structural quality of grown HEMT structures and electrical characterization techniques like I-V measurement & Hall-effect measurement. In the experimental part, the surface morphology of the AlGaN/GaN-HEMT structures has been characterized using Atomic Force Microscopy (AFM) technique. AlGaN/GaN- HEMT structures have shown mound type of surface morphology with average mound sizein the range of 1.7 μm to 2 μm and mound height in the range of 9nm to 26nm. The surface morphology of AlGaN/GaN-HEMT structures was found to be changing with the GaN growth rate. A linear increase in the surface roughness was observed with the increase of growth rate. Furthermore, screw type dislocation density was found to be present in AlGaN/GaN HEMT structures and the pit density on the surface was estimated to be 2.6 x 10-9 cm-2. Hall measurements were performed on AlGaN/GaN HEMT structures and the average mobility, sheet concentration and sheet resistivity values were obtained as 1140 cm2/V-s, 1.237 x 1013/cm2 and 442 ohm/sq. respectively. Annealing of AlGaN/GaN HEMT structures resulted in decrease of the vertical leak current, however, 2DEG properties found to be destroyed. Carbon doping GaN buffer layers in AlGaN/GaN HEMT structure resulted in reduction of vertical leakage current with slight reduction of 2DEG properties.