New insights into the compensation mechanism of Fe-doped InP

Abstract

We have investigated iron-doped semi-insulating and conducting InP using a variety of characterization techniques. The occupation of the iron acceptor level was determined from measurements of the Fe2+ intracenter absorption and the Fe3+ electron paramagnetic resonance signal. These iron concentrations were then related to the total iron content, the free carrier concentration, and the net donor concentration as determined from an impurity analysis. When comparing the sum [Fe2+]+[Fe3+] with the total iron content of the samples measured by glow discharge mass spectroscopy we find that below about 1×1017 cm−3 no significant formation of precipitates occurs. Analysis of the free carrier concentration in semi-insulating crystals allows us to determine the temperature shift of the iron acceptor level with respect to the conduction band. We obtain a value of 4.7×10−4 eV/K somewhat larger than the band-gap shift of InP (3.8×10−4 eV/K). Due to this temperature shift the thermodynamic position of the iron acceptor level at room temperature is about 0.49 eV below the conduction band. This value is significantly smaller than the low temperature value of 0.63 eV. We believe that the temperature shift of deep electronic levels provides insight into the local electron-phonon coupling. Finally we find that the net donor concentration determined by an impurity analysis appears to be too low to account for the observed [Fe2+] concentrations. We present evidence that the missing donor is related to the well-known hydrogen related local vibrational mode at 2315 cm−1. These results indicate that both hydrogen passivation and native defects are necessary for a quantitative understanding of the compensation mechanism in semi-insulating InP.

Direct recognition of non-radiative recombination centers in semi-insulating LEC InP:Fe using double excitation photoluminescence

“…This result is quite consistent with the shrinkage in energy band gap of InP crystal doped with Fe [13,17]. The luminescence peak at 1.416 eV energy is due to transition between band states and shallow donors [17][18][19][20][21] and is very close to the band gap energy of InP. The peak at 1.380 eV is thought to be a transition from a shallow donor to a shallow acceptor pair, and band to acceptor [20][21][22][23], and the peak at 1.337 eV is a phonon replica that appears at 43 meV lower energy than the 1.380 eV peak [22,23].…”

“…The energy level occurring at 0.65 eV has been identified as a deep Fe 2+ /Fe 3+ acceptor level. The activation energy of this center is in good agreement with the energy of the transition Fe 2+ -Fe 3+ +e À to the conduction band [18,26].…”

Dislocation cell structures in melt‐grown semiconductor compound crystals

“…S, Zn > 10 18 cm -3 ) can prevent the cell formation process totally due to the minimization of the dislocation movement [67]. Fe, however, cannot be used as effective mobility "stopper" because of its low solubility limit of ~ 10 17 cm -3 in InP [68]. Well-distinguishable networks of grains with dimensions of 2 -10 µm can be forced in undoped InP crystals by post-growth mechanical bend higher than 20 MPa and temperatures over 800 °C [52].…”

Phosphorus–hydrogen complexes in LEC‐grown InP

“…This has been discussed to be relevant for the charge compensation of residual donors by doping with iron [14,15]. However, there are no experimental data for the level positions of these two defects in the gap of InP.…”