Designs for adapting a ladder rail so that accessories to the ladder can be quickly and securely mounted and released without using tools. The active layer 12 has, at least, a barrier layer 2a having an n-type impurity, a well layer 1a made of a nitride semiconductor that includes In; and a barrier layer 2c that has a p-type impurity, or that has been grown without being doped. Apparatus for accessing electronic currency is also described. The cold shield has an upper cold shield member for holding the lens assembly and a lower cold shield member for holding the focal plane array.