The Doping and Characterization of Erbium-Implanted GaN
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Mat. Res. Soc. Symp. Proc. Vol. 482 0 1998 Materials Research Society
InGaAs laser diode (983 nm) was pulsed at 25 Hz. Reverse biased GaN:Er,O metal-insulator-ntype (m-i-n) light emitting diodes (LEDs) were used for the EL measurements. 1.4EL time-decay was measured using square wave pulse c-" 1.2 excitation at 20 Hz. The GaN:Er,O LED fabrication and cc, 1.0 performance is described elsewhere.[4] The Er o 0.8 luminescence was collected by a lens (numerical aperture = 0.5) c 0.6 through a 32 cm single-pass 0 grating (blazed at 1.5 gm) m 0.4 monochromator, and detected 02 using a thermoelectrically L. 0.2 cooled InGaAs photodiode. For 0.0 the PL measurements a bandpass filter (1500 nm - 1650 nm)was 100 150 200 250 50 0 placed in front of the detector. Depth (rv) The PL and EL signals were measured with a lock-in Fig.1. Implantation profile for a sample amplifier and recorded using a implanted with [Er2] 2x1015 ions/cm2. computer. For the time-resolved measurements, the PL and EL signals were recorded and averaged using a digitizing storage oscilloscope. The room temperature luminescence data shown below were not corrected for the spectral responses of the bandpass filter or the detectors, although the corrections are less than 20% over the wavelength range of interest (1500 - 1600 nm). Three different excitation methods were employed. For pumping at 983 nm, 514 nm and 488 rm, the GaN is transparent and the Er ions are pumped directly to excited energy levels (4115/2 -> 4111/2, 2H11/2, 4F7/2 ). With pumping at 351 rn and 368 run, electrons are excited across the bandgap of GaN (3.4 eV at room temperature) and the subsequent Er-excitation mechanism is assumed to be an electron-hole pair mediated process.[10] During EL, in strongly reverse biased m-i-n LEDs, highly energetic electrons are injected into the Er-implanted i-GaN region and the primary excitation mechanism is assumed to be impact excitation. Electron-hole pairs are also formed, but the cross section for impact excitation is five orders of magnitude larger than an electron-hole mediated process. [4] RESULTS The Er-related PL (983 nm pump) and EL (-300 p.A) time decays were studied at room temperature. No PL at 980 nm was seen from any of the samples. A typical PL decay trace (at 1539 am) exhibiting a 2.33 ms 1/e lifetime is shown in Fig. 2. Strong PL was detected from the GaN:Er,O films only after annealing above 900 0C in NH 3 (Fig. 2 inset). The error in the lifetime measurement was +/-5%. The single exponential decay, and the long lifetime is evidence of a highly efficient radiative process. For comparison the PL lifetime of GaN:Er,O for a 337 am pump was 2.15 ms +/-5%.[9)
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Time (ms) Fig. 2. PL time decay for 1539 nm light from GaN:Er,O. Inset shows PL spectrum.
Fig. 3. EL t
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