Plasma frequency in doped highly mismatched alloys*

Group III-nitride alloys are the prototypical examples of highly mismatched alloys (HMA), where the alloying element with significantly different electronegativity (e.g., nitrogen) forms localized defect states. These defect states couple to extended states of the host semiconductor and create two split bands; the lower split band has been used as an intermediate band for intermediate band solar cells. We consider a HMA with such a conduction band anticrossing where the lower split band is partially filled by doping. The mobile electrons in the lower band sustain plasmonic oscillations, and we show that they behave differently than their counterparts in metals and semiconductors due to the anomalous state distribution in the split bands of HMAs. We use a spectral density for HMAs to build a model that allows study of the effects of the state distribution on the bulk plasma frequency. We solve our model semi-analytically and show that interband effects of the upper split band bound the plasma frequency to be smaller than an effective band gap. We focus on GaAsNP quaternaries and show their special appeal for mid-infrared plasmonic applications due to their high tunability and the presence of an energy gap between the two split bands.