OFF-CENTER D- CENTERS IN A QUANTUM-WELL IN THE PRESENCE OF A PERPENDICULAR MAGNETIC-FIELD - ANGULAR-MOMENTUM TRANSITIONS AND MAGNETIC EVAPORATION

We investigate the effect of the position of the donor in the quantum well on the energy spectrum and the oscillator strength of the D- syst em in the presence of a perpendicular magnetic field. As a function of the magnetic field, we find that when D- centers are placed sufficien tly off-center, they undergo singlet-triplet transitions which are sim ilar to those found in many-electron parabolic quantum dots. The main difference is that the number of such transitions depend on the positi on of the donor, and only a finite number of such singlet-triplet tran sitions are found as a function of the strength of the magnetic field. For sufficiently large magnetic fields the two-electron system become s unbound. For the near center D- system, no singlet-triplet transitio n and no unbinding of D- is found with increasing magnetic field. A ma gnetic field vs donor position phase diagram is presented that depends on the width of the quantum well.