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Study on trapping center and trapping effect in MSM ultraviolet photo‐detector on microcrystalline diamond film

A MSM (metal‐semiconductor‐metal) ultraviolet (UV) photo‐detector was fabricated on a high‐quality diamond film deposited by microwave chemical vapor deposition on a Si substrate. Charge‐based deep level transient spectroscopy (Q‐DLTS) was used for obtaining the information on activation energy (Ea), capture cross section (σs) and concentration (Nt) of trapping centers in the band gap of the diamond film. A shallow level with Ea = 0.213 eV, σs = 9.88 × 10−20 cm2 and Nt = 1.1 × 1011 cm−2 is present in the diamond film. The shallow level may not act as effective recombination center due to the so small activation energy according to the Schockly‐Read‐Hall statistics. The UV photo‐detector presents slow time response, high responsivity and high photoconductive gain under irradiation of 220 nm monochromatic light. These performances indicate that minority carrier trapping effect may play an important role in the UV photo‐detector. The photo‐generated minority carriers (electrons in this work) may be trapped by the shallow level during light irradiation process and then de‐trap slowly via thermal excitation or tunnelling effect after removing the light source, which contributes to the prolonged response time. The trapping effect can also reduce the carrier recombination probability, resulting in the high responsivity and high photoconductive gain.