Quantum efficiency measurements and modeling of ion-implanted, laser-annealed charge-coupled devices: x-ray,...

We report quantum efficiency measurements of backilluminated, ion-implanted, laser-annealed CCD's in the wavelength range 13-10,000 Å. The equivalent quantum efficiency (the equivalent photons detected per incident photon) ranges from a minimum of 5% at 1216 Å to a maximum of 87% at 135 Å. Using a simple relationship for the charge-collection efficiency of the CCD pixels as a function of depth, we present a semiempirical model with few parameters that reproduces our measurements with a fair degree of accuracy. The advantage of this model is that it can be used to predict CCD quantum efficiency performance for shallow backside implanted devices without a detailed solution of a system of differential equations, as in conventional approaches, and it yields a simple analytic form for the charge-collection efficiency that is adequate for detector calibration purposes. Making detailed assumptions about the dopant profile, we also solve the current density and continuity equations in order to relate our semiempirical model parameters to surface and bulk device properties. The latter procedure helps to better establish device processing parameters for a given level of CCD quantum efficiency performance.