The author presents simple designs of quantum-well-based detectors which can be easily fabricated and which can detect a flux of X-rays incident on the detector. The author calculates the X-ray induced change in absorption and refractive index in GaAs-based quantum wells and uses that information to predict the performance of several proposed X-ray detectors based on carrier induced change in optical susceptibility in semiconductor quantum well structures following X-ray absorption. A 1% change in the probe beam in a reflection geometry is calculated for an incident flux of 12 X-ray photons per mu m/sup 2/.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>