GaAs Quantum Well Laser

Abstract

As an example of a bipolar semiconductor laser, we treat the GaAs quantum well laser (wavelength around 800 nm). In later chapters, we will study quantum well lasers consisting of other materials and bipolar lasers of other types.

Problems

22.1

Quasi-Fermi energies. A quantum film contains nonequilibrium electrons and holes. Determine the electron density at which the difference of the quasi-Fermi energies is 3kT (T $=$ 300 K). [Hint: make use of the figure concerning the Fermi energies.]

22.2

Quantum well laser. A GaAs quantum well laser (length 0.5 mm, width 0.2 mm, resonator height 500 nm) contains 3 quantum wells and is operated at room temperature. Estimate the threshold electron density, threshold current density and threshold current. [Hint: neglect thermal broadening of the gain curve.]

22.3

Photons in a quantum well laser. A GaAs quantum well laser (length 0.5 mm, width 0.2 mm, resonator height 500 nm) contains 3 quantum wells, is operated at room temperature and emits, in two directions, laser radiation of a power of $P_\mathrm{out} =1$ mW into each of the directions.

• (a) Determine the photon density in the resonator.

• (b) Determine the total photon number $Z_\mathrm{tot}$ in the resonator.

• (c) Compare $Z_\mathrm{tot}$ with the total number of nonequilibrium electrons in the quantum film.

22.4

Vertical-cavity surface-emitting laser. A vertical-cavity surface-emitting laser contains a GaAs quantum well and another laser contains five quantum wells; $(f_2 - f_1)_\mathrm{th} =0.5$ and $\tau _\mathrm{sp} =8 \times 10^{-9}$ s. Determine the following quantities:

• (a) Threshold reflectivity of the output coupling mirror.

• (b) Threshold current.

• (c) Threshold current density.