Optical characteristics of highly-strained gaInNAs qauntum well

Abstract

The band structures, gain characteristics and thermal properties of GaInNAs, InGaAlAs, and InGaAsP single quantum well structures for 1.3-㎛ emission wavelength are studied and compared. For GaInNAs, two models for band structures are used. One is the linear interpolation model and the other is the band anti-crossing model. In the former model, the conduction and valence band edge of $Ga_{1-x}In_{x}N_{y}As_{1-y}$ are given by subtracting the energy difference between the band edges of GaAs and $GaN_yAs_{1-y}$ from those of $Ga_{1-x}In_{x}As$. The other material parameters are assumed to be same as those of $Ga_{1-x}In_{x}As$ for small nitrogen compositions. Among the lots of composition combinations with same emission wavelength, the high-In and low-N GaInNAs quantum well exhibits a larger optical gain, larger differential gain, and smaller carrier leakage than the low-In and high-N GaInNAs quantum well because of the strain. For example, more than a two-fold improvement in threshold current density is expected from the high-In and low-N quantum well laser than the low-In and high-N quantum well laser. In the latter model, the conduction bands of GaInNAs are calculated from the coupling between the $Ga_{1-x}In_{x}As$ electron states and highly localized nitrogen states. Because the localized nitrogen states does not interact with the states in the valence band, the transition matrix elements of GaInNAs are small. But, the large electron effective mass and energy spacing between sub-bands increase the differential gains. It improves the high-speed modulation properties and reduces the threshold carrier density for applications that require large gain such as VCSEL. To understand the thermal characteristics of GaInNAs, InGaAlAs and InGaAsP, the temperature-induced shift of the band gap energy is estimated by the Barshni’s model. The larger conduction band offset and larger energy difference between the well and barrier structure produce a higher barrier height in ...