Dilute Nitrides

Dilute nitride and extreme semiconductor alloys

Electronic Structure Dilute NitridesDilute nitrides are a novel class of semiconductors that have been doped with small concentrations of nitrogen to change their electrical and optical properties. A dilute nitride material of particular interest is GaInNAs, often pronounced "Guinness", like the drink. The introduction of nitrogen into GaInAs causes a drastic reduction in the band gap and hence a lengthening (or red shift) of the wavelength of light associated with it. At the same time, the relation between the energy and momentum of electrons is profoundly changed, which in turn changes the electrical properties of the material in a high electric field.

The novel electronic structure of dilute nitride alloys open a wide range of potential applications, including:

  • GaAs-based lasers and optical amplifiers at telecommunication wavelengths
  • Highly efficient multi-junction solar cells
  • Microwave and terahertz technology using the novel band structure
  • Low-noise avalanche photodetectors with suppressed electron multiplication

 

Fig. 1 Variation of energy gap (lower curve) with composition in GaNxAs1-x.

Electronic Structure and Transport Properties

We have led the development of theoretical models of the band structure and transport and optical properties of dilute nitride alloys. The reduction in energy gap in GaNAs was initially explained in terms of a band-anticrossing (BAC) interaction between the GaAs conduction band edge and a higher-lying band of N resonant states. We justified the basic principles of the BAC approach [1] but showed that it needed to be extended to treat the interactions between the band edge and a distribution of N states in GaNAs and related alloys [2,3]. This enables a quantitative description of many of the electronic properties, including the unexpectedly large electron mass [4] and low mobility [5] observed in GaNxAs1-x. Ab initio calculations have been carried out the allow us to understand the local vibrational modes of nitrogen clusters [6], and the mechanical properties of dilute nitrides [7].

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