DONOR-EXCITED STATES AND INFRARED-TRANSITION STRENGTHS IN CYLINDRICALGAAS-(GA,AL)AS QUANTUM-WELL WIRES

A variational calculation within the effective-mass approximation of t he ground and lowest excited states of a donor impurity in a cylindric al GaAs-(Ga,Al)As quantum-well wire is presented. The corresponding im purity binding energies are calculated for various values of the GaAs- (Ga,Al)As quantum-wire radius and donor positions within the wire. The line strengths of transitions from the donor ground state to excited states of 2s-like and 2p(z)-like symmetries are calculated as the dono r position varies along the radial direction in the wire, for polariza tions of the incident radiation perpendicular and parallel to the wire axis, respectively. Although the 1s-->2s donor transition is forbidde n in bulk materials, this transition is allowed for incident radiation polarized along the y radial direction of the wire with a quite consi derable oscillator strength-comparable to the strength of the 1s-->2p( z) transition-for impurities away from the wire axis.