For the first time, the electro-optical properties of nontetrahedrally bonded crystalline and amorphous polyphosphides have been investigated. The crystalline archetype KP15 is a high resistivity semiconductor, with photoconductivity and photoluminescence at the band gap (1.7 eV). These measurements are extended to amorphous films prepared by vapor transport methods. The resistivity of the films has been varied over eight orders of magnitude by the incorporation of 0%–2% Ni. Nonlinear metal-semiconductor behavior with good current carrying capability (1 A/cm2) has been observed. When deposited on InP, the films reduce the density of surface states in metal-insulator-semiconductor diodes to ∼1010/cm2 eV, probably by providing continuity to the group V element at the interface. It is concluded that the low crystal symmetry of polyphosphides leads to a significant new amorphous semiconductor in which the electronic coherence length is commensurate with the intermediate range order.
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High-speed, 80-μm-diam, GaAs/Alx Ga1−x As p-i-n photodiodes having frequency response in excess of 7 GHz and internal quantum efficiency approaching 100% were fabricated by low-pressure metalorganic chemical vapor deposition (MOCVD) using both tertiarybutylarsine (TBA) and arsine. These are the highest performance MOCVD GaAs devices achieved with nonarsine sources and comparable to the best reported p-i-n photodiodes of similar size. Net carrier concentration of the undoped TBA GaAs was determined by capacitance-voltage analysis to be less than 5×1014 cm−3 . Photoluminescence measurements indicate that undoped TBA-grown Alx Ga1−x As (x=0.25) is also of excellent quality (FWHM=12 meV). Growth conditions leading to optimized devices were found to be similar for the two sources.
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