Subband nonparabolicity estimated from multiple intersubband absorption in highly doped multiple quantum wells

We report strong room-temperature intersubband absorption in 80 Å strain-compensated ${\mathrm{In}}_{0.84}{\mathrm{Ga}}_{0.16}{\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}\mathrm{A}\mathrm{s}/\mathrm{I}\mathrm{n}}_{0.52}{\mathrm{Al}}_{0.48}\mathrm{As}$ double-barrier quantum wells grown on InP substrates. From the multiple Γ-Γ intersubband transitions observed, it is inferred that the electron effective masses and nonparabolicity parameters for the first two subbands differ significantly from each other. For the range $k\sim 5\times {10}^6–6\times {10}^6{\mathrm{cm}}^{-1},$ the difference in subband parameters results in a change in transition energy of about twice the value calculated for the corresponding GaAs/AlGaAs quantum well.