Donor-acceptor pair recombination

Leite, R. C. C. DiGiovanni, A. E. 1967. Frequency shift with temperature as evidence for donor-acceptor pair recombination in relatively pure n-type gallium arsenide. Phys. Rev. 153 841-843. 

Another feature clearly observed in FIGURE 1 is the sharp transition on the low energy side of the I2 line and labelled I2 (n = 2). It is interpreted as a two electron satellite of the donor bound exciton line, i.e. due to a recombination where the donor is left in its n = 2 excited state [6,19], From the 22 0.5 meV separation from the I2 line, a donor binding energy of 29 1 meV can be deduced [6,19], The weak transitions in FIGURE 1 at 3.27 and 3.18 eV, attributed to donor-acceptor pair recombinations, are discussed below. 

The EPR spectrum of the intrinsic STH was also recorded by ODMR in studies of nominally pure AgCl [171,172] and was later identified [173-175]. The self-trapped hole and shallowly trapped electron undergo donor-acceptor pair recombination which contributes to a blue-green (500 nm) luminescence from AgCl [69]. The species observed in the ODMR spectrum has g-factors, hyperfine, and superhyperfine matrices that are identical, within experimental error, to those observed earlier by EPR methods [68]. 

Blue LEDs made in the 6H-SiC polytype, utilising a donor-acceptor pair recombination, are now commercially available. Boron-doped 6H-SiC produces a yellow colour while green... 

We have studied the synthesis of InAs nano-sized crystalline precipitates in crystalline silicon by means of the co-implantation of As+ (245 keV, 5xl016 cm2) and In+ (350 keV, 4.5xl016 cm 2) at 500 °C and annealing at 900 °C for 45 min. RBS, TEM/TED and PL techniques were used to characterize the implanted layers. The density of the precipitates equals to 1.2xlOn cm 2. The most of the crystallites are from 2 nm to 8 nm in size. The precipitates are located within at the depths of 100 to 350 nm. A broad line at 1.3 pm is found in low-temperature PL spectra of co-implanted and annealed silicon crystals This line can be attributed to donor-acceptor pair recombination between In and As atoms which occupy the substitutional sites in the silicon lattice. 

The broad PL band at 0.988 eV is registered in PL spectra of the annealed samples (spectrum 2). The high-energy tail of this band contains many narrow lines (shown in the inset more detail). A similar emission band and narrow lines were detected previously in silicon crystals doped with P and In by thermal diffusion. As shown in [2], the recombination involving P and In centres separated by distances from 0.77 to 2 nm is responsible for the observed sharp line structure. In our experiment part of In and As atoms occupy regular sites in the Si lattice after annealing. In our opinion these spectra (narrow lines and broad band at 0.985 eV) are due to donor-acceptor pair recombination between In (acceptor) and As (donor) separated by the distance from 0.6-2.5 nm. 

This degrades the recombination efficiency as the quality of the p-type material is inferior. PL and absorption (transmission) measurements performed in the same structure indicate the EL emission to coincide with the PL band at 440 nm, which is thought to represent the donor-acceptor pair recombination in p-type ZnO. To circumvent this problem, the p-doping level must be increased and/or heterojunction wherein the recombination occurs irrespective of the relative doping levels should be controlled. 

The excitation intensity was also varied in order to determine the effect this had on the PL spectrum. PL1 and PL3 bands had a blueshift per decade of 3.7 meV and 5.5 meV, respectively, with an increase in excitation intensity. The blueshifts were attributed to donor-acceptor pair (DAP) recombination.68,69 PL2 did not show any excitation power dependency, whereas the analysis of the PL4 band was not attempted because of the uncertainty in its precise location. The effect of increasing excitation intensity can be clearly observed in Fig. 6.29. 

The primary objects of investigation in both TSL and TSC experiments are nonra-diative transitions between the ground level and trap and the conduction band and/or valence band. In a case when two different impurities—a donor and an acceptor—are close enough that their functions overlap, tunneling processes may take place from an excited level of the donor to the acceptor. In this case, the excited level can be occupied from the ground state via a nonradiative transition. In a case when recombination traffic proceeds via tunneling between donor-acceptor pairs, no TSC will be observed. 

Tunneling recombination of donor-acceptor pairs in crystals... 

Ideas about the tunneling mechanism of the recombination of donor acceptor pairs in crystals seem to be first used in ref. 51 to explain the low-temperature of photo-bleaching (i.e. decay on illumination) of F-centres in single crystals of KBr. F-centres are electrons located in anion vacancies and are generated simultaneously with hole centres (centres of the Br3 type which are called H-centres) via radiolysis of alkali halide crystals. 

TUNNELING RECOMBINATION LUMINESCENCE OF DONOR-ACCEPTOR PAIRS... 

Recombination of the surface electron Fs+ -centres and of the bulk hole V -centres in y-irradiated highly dispersed oxide CaO has been studied [69]. The recombination kinetics is weakly dependent on temperature in the range 4.2-77 K. The formal activation energy has a value of only 30 cal mol l. At small irradiation doses (less than 2 x 1019eVcm-3) the recombination appears to be of geminate character, i.e. it occurs only in the parent donor-acceptor pairs, the process kinetics being well described by the linear dependence of the concentration of centres on the logarithm of observation... 

FIGURE 9.1 Schematic of emissive transitions of electrons in semiconductors (a) band-band emission (b) a free electron recombines with a trapped hole (c) a trapped electron recombines with a free hole (d) donor-acceptor pair emission. 

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