| Summary: | 碩士 === 國立交通大學 === 電子物理系 === 88 === We have studied the isoelectronic (In and As) doping effects on the optical characteristics of GaN films by time-integrated and time-resolved photoluminescence. For undoped GaN with a buffer layer of 35 nm and 60 nm, the decay time of neutral-donor-bound exciton (I2) transition increases with T1.5. From the Shockley-Read-Hall (SRH) model, we can deduce the relationship between the lifetime and the trap concentration. The GaN of 60 nm buffer thickness appears to have 3 times more trap concentration than that of 35 nm one. For In-doped GaN, we have observed the decay time of the I2 line that is almost independent of the temperature and In source flow rate. These observations might be attributed to the intrinsical characteristics of isoelectronic In doping. For As-doped GaN, the I2 decay time first decreases exponentially from 105 ps to 40 ps between 10 K and 75 K, and then increases gradually to 72 ps at 250 K. Such a difference is related to the isoelectronic As impurities itself in GaN, which generate near-by shallow levels that predominate the recombination process.
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