| Abstract [eng] |
Gallium nitride (GaN) is a promising material for next generation electronic and photonic devices. GaN has a wide direct bandgap (3,4 eV) which is tunable from infrared to ultraviolet spectrum by mixing nitride with additional group III elements. Its superior material properties such as high breakdown electric field and good thermal conductivity make it suitable for high-temperature, high-frequency and high-power device applications. Acceptable resistance to ionizing radiation enables GaN-based devices to be exploited in extreme environments and even function as radiation sensors. GaN technology is still relatively new and there has been a lot of effort to optimize it. Different sensor geometries are proposed and evaluated by numerous groups. In this work the growth and processing of GaN p-i-n diodes are demonstrated. Relatively thick (32 µm) GaN layers were grown using metalorganic chemical vapor deposition technique with process interruptions. Thick GaN as well as doped p and n-type GaN layers were grown on sapphire substrates. Two distinct sensor geometries were chosen for further device fabrication – mesa type and sandwich type. Many manufacturing processes were carried out to achieve desired shapes and geometries. Laser lift-off was used to separate GaN from the substrate. Different transfer techniques were tested. Dry etching was employed to fabricate mesa structures. E-beam deposition and wet etching were performed for fabrication of metal contact layers. To find out optimal parameters for each processing step, variety of measurements were carried out. Transmission line model (TLM) were used to determine sheet and specific contact resistances. It was found that post-growth contact annealing in oxygen-containing atmosphere facilitates in activating Mg dopants and increasing p-type GaN electrical conductivity. Optical microscopy and image analysis revealed how inert and halogen gases influence uniformity of dry etching. Two sets of sensors (mesa and sandwich type) were fabricated using optimized processing conditions. Electrical measurements revealed diode-like current-voltage characteristics of GaN p-i-n devices. Fabricated sensors are now ready for further testing in increased radiation environment. |
