Magnetic field-induced suppression of acoustic phonon emission in a superlattice

We analyze theoretically the influence of magnetic field on the electron lifetime in the excited state of a specially designed superstructure allowing electron injection into the excited miniband. We show that the discrete electron energy spectrum arising in the magnetic field dramatically suppresses the acoustic phonon emission rate and gives rise to electron accumulation in the excited subband. This can be used for obtaining stimulated emission between minibands as well as between Landau levels. The latter is of particular interest since the energy of this radiation can be varied by magnetic field. We also obtain an oscillatory dependence of electron lifetime in the excited state on magnetic field which can be verified in a simple photoluminescence experiment. Finally, we extend our considerations to the case of quantum dots, capable of providing complete energy quantization in the absence of magnetic field.