SPRInG is an Innovative Training Network supported by the Marie Skłodowska-Curie Actions. Shaped by the European Industrial Doctorates programme, SPRInG offers joint research training at the PhD level by the collaboration of academic and non-academic organizations. SPRInG objectives are the exploration of the formation mechanisms and the investigation and mastering of the structural and optical properties of rational (In,Ga)N in the form of SPSLs.

 

(In,Ga)N layers are widely used as the active region in a large variety of optoelectronic devices. The direct band gap of these alloys, ranging from 0.63 eV (InN) to 3.45 eV (GaN), makes them highly attractive for light emitters covering almost the full spectral range. As a fundament for the high performance of such devices, the fabrication of (In,Ga)N multiple quantum well (MQWs) heterostructures with high quality significantly improved over the last three decades, and enabled for instance the fabrication of state of the art white light-emitting diodes (LEDs) with very high efficiencies. However, particular applications such as laser diodes (LDs) are more demanding and require not only high crystalline quality but also a very uniform material that generates a homogeneous potential within the MQWs.

 

Recently the concept of “rational” (n InN/m GaN) structures based on short period superlattices (SPSLs) stacking integer numbers of m (n) monolayers (ML) of InN (GaN), i.e. heterostructures of pure InN MLs embedded in a GaN matrix, have been proposed in order to handle these challenges. Such structures also called “digital alloys”, in contrast to the routinely formed “random (In,Ga)N alloys” are very promising for use as active regions in optoelectronic devices because:

 

  • The growth of single InN MLs on top of GaN should limit the generation of misfit dislocations at the heterointerfaces,
  • The emission wavelength could be  tuned by changing the barrier thickness for coherent growth of rational (1InN/mGaN),
  • The Quantum Confined Stark Effect should be reduced in ultrathin wells,
  • InN and GaN intermixing should be minimized by self-ordering and phase-separation mechanisms, providing for sharp heterointerfaces.

 

Our project “SPRInG” has for scientific mission to develop a novel (In,Ga)N alloy that offers completely new opportunities to tune bandgaps and piezoelectric fields in quantum structures for highly efficient optoelectronic devices. The development of fundamental knowledge on rational (InN/GaN) alloys as established for other III-V compounds is envisioned as the base for such devices.