In 1995, Meyer et al. proposed a four-constituent type IIb quantum well heterostructure, which is now known as the "W" well, because the conduction band edge of the heterostructure is shaped like the letter W. The W-well structure consists of a hole-confining region sandwiched between two electron-confining regions.
The optical pumping injection cavity (OPIC), proposed and demonstrated by C. L. Felix et al. at the Naval Research Laboratory in Washington, D.C. in 1999, is used to enhance the absorption of the pump beam. In an OPIC device, the active region is enclosed between two Bragg reflectors (or quarter wave stacks), forming an etalon cavity for the pump beam. When both the W active region and the optical pumping injection cavity are found together, the resulting laser is called a "W-OPIC" laser. My dissertation research uses a tunable source (optical parametric oscillator) to resonantly pump W-OPIC semiconductor laser devices with varying cavity length. The output beam is directed through a window in the refrigerated vacuum shroud and collected by a short focal length lens and focused onto either a photovoltaic indium antimonide detector to measure the radiative power output of the laser for light-light curve measurements or reflected and focused onto the entrance slit of a diffracting spectrometer so that the spectrum of the output beam may be measured.
The resulting spectra from one of these lasers demonstrate a linear redshift of 1.437 ±0.018 nm/K as the temperature increases from 77 K to 325 K. Such behavior is attributed to both the changes in the band gaps of the constituent materials as the temperature increases as well as the changes in the semiconductor layer thicknesses due to thermal expansion. The former affects the barrier height of the quantum wells and the latter affects the width of the quantum wells. Since changes in either of these parameters affect the value of the energy levels in a quantum well, the energy of the lasing transition will also change.
This project is intended test the validity of this claim in a qualitative way. The confinement of electrons in the quantum well is easily modeled by a modification of the textbook finite quantum well problem. Solving for hole confinement is quite a bit more complicated because of a large degree of mixing between the heavy and light hole bulk states. Though a full treatment would be well beyond the scope of this project, a simplified model, which neglects the mixing between the valence band bulk states, may be used to compute the energy levels of electrons in the conduction band of the W-well and holes in the valence band of the W-well for the varying barrier heights and well widths that nominally result from variation in the temperature of the semiconductor material.