Dilute magnetic semiconductors(DMSs)

such as MnGaAs

MnCdTe

CoZnO

and FeZnO

offer the great opportunity to integrate the magnetic

electrical

and optical advantages into a single semiconductor material. Therefore

DMSs attract more and more interests for the application in spintronics field. However

incorporation of transition metal ions will inevitably effects on the optical and electrical properties when the magnet functionalities are introduced into semiconductors. Besides the quenching behavior in fluorescence due to the complex energy level system

the effect of transition metal ions on conduction of the matrix is not neglectable because of the alterable valence. In present work

we found that doping of Fe ions changes the conduction type of the CdS thin films form n-to p-type. The Fe related donor-acceptor pairs emission was discussed by photoluminescence (PL) characterization. Cd

1-x

Fe

x

S thin films with different Fe contents were grown on c-plane sapphire substrate by low-pressure metal organic chemical vapor deposition. Dimethyl cadmium

iron pentacarbonyl and H

2

S were used as precursors

flow rates of which were fixed at 3.51×10

-6

3.77×10

-7

and 1.62×10

-5

mol/min by separate mass-flow controllers

respectively. High purity hydrogen (99.999%) was used as carrier gas with total flow rate of 1.9 liter/min. The growth was performed for 30 min

and the thickness of samples ranges from 500 to 700 nm. A Lake Shore 7707 Hall measurement system was employed to measure the electrical properties of the thin films. PL measurements were performed on a JY-630 micro-Raman spectrometer in a backscattering geometry configuration. The excitation source for the PL is the 325 nm line of a He-Cd laser. The Fe contents in samples A

B

C

D

and E are 0.0025

0.0072

0.0149

0.0455

and 0.1400

respectively

which were measured by energy dispersion spectroscopy. The resistivity of the thin films was found to increase with the addition of more Fe contents into the Cd

1-x

Fe

x

S thin films

and eventually the conductivity of Cd

1-x

Fe

x

S thin film reverses from n-to p-type at high density Fe doping. Because the samples were Cd-rich

the acceptors can be only offered by Fe ions doped into the CdS films. The p-type conduction was attributed to the ionization of holes from trivalent Fe ions

which was formed by the oxidation of Fe

2+

ion near the sample surface. With increasing Fe content

the band-to-band transition at 2.5 eV was suppressed while the emission located at 2.0~2.4 eV finally dominated the PL spectra. Under various excitation density

the PL emission located at 2.0~2.4 eV shows significant evolvement. The intensity of high-energy side of this emission increases more rapidly than that of the low-energy side with increasing excitation density. Therefore

the emission at 2.0~2.4 eV was attributed to donor-acceptor pairs. According to the PL peak position and carrier density obtained by electrical measurement

the energy level of Fe acceptor was calculated to be about 320 meV by using the formula.