III-Nitrides alloys (GaN, InGaN, AlGaN and AlInGaN) are widely used for several applications, such as High Electron Mobility Transistors (HEMT), solar cells, light emitting devices. These alloys show a bandgap tunable with composition, covering the whole visible spectrum; however, these materials suffer from the presence of structural defects emerging from strain and thermal relaxation phenomena. We study transport properties, optical spectra, electrical properties at macro and nano-scale and quantum confinement effects in order to clarify the role of material properties on device behaviour.
The III-Nitrides materials system has impacted energy efficiency on the worldwide scale through its application to blue light-emitting diodes (LEDs). This impact on technology and society was recognized by the award of the 2014 Nobel Prize in Physics to Isamu Akasaki, Hiroshi Amano, and Shuji Nakamura. The binary nitrides cover a wide range of direct band gap energies with energy gap tunable by alloy composition ranging from 0.65 eV (InN) to 6.0 eV (AlN). However, the large mismatch in lattice constants between the nitrides and their substrates results in highly strained heterostructures with ternary alloys. This strain can lead to defect formation, reduced material quality, and polarization-related electric fields in basal plane growth.
We study how strain relaxation and defect formation affect material and device quality.
The graph shows band gap energy versus lattice constant for III–V and II–VI semiconductors. Open circles indicate indirect band gap materials. InGaN and AlGaN ternary alloys span a large range of lattice constants. from Leah Y. Kuritzky James S. Speck , MRS Communications, Volume 5, Issue 3, September 2015 , pp. 463-473.
Surface Photovoltage spectra of InGaN/GaN heterostructures with different In%. The spectra shows the GaN band gap, which keeps constant, while the InGaN gap varies as a function of In content.
Published on: Materials Science in Semiconductor Processing, 2018, https://doi.org/10.1016/j.mssp.2018.05.027
Electronic transitions in low dimensional semiconductor structures measured by surface photovoltage spectroscopy
Daniela Cavalcoli Maria Antonietta Fazio