A heterojunction semiconductor device including an array of microstructures, each microstructure including a microwire of a first semiconductor material and a coating of a second semiconductor material forming a heterojunction with the microwire; a first electrical contact and a second electrical contact, one of which is connected to the microwire and the other of which is connected to the coating, is described. Also described are considerations for configuring the array of microstructures, and methods of forming the array of microstructures.
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 This invention may have been made with government support awarded by the U.S. Department of Energy. The government may have certain rights in the invention.