Gallium Phosphide (GaP) is known as one of the basic optoelectronic material since more than 30 years. Its light emitting features in a visible spectral range were intensively studied in the second half of the twentieth century. Lately GaP has been found to be also interesting material in dynamically developed infrared optic [1]. For this application undoped of high purity material is necessary. The growth of undoped GaP by liquid encapsulated method (LEC) showed that its electrical parameter can be changed not only by residual dopants distribution.

To understand the change of the electrical parameters along the length of GaP crystal or during its annealing one needs to assume the creation of electrically active native defect related centers. The purpose of this paper was to explain what kind of defects it can be.

Undoped GaP grown by LEC method was studied. The residual electrically active dopants in GaP grown by this method were silicon, carbon and oxygen. Carbon and oxygen amount was controlled by the intensity of low temperature local vibrational mode absorption (LVM) at 605.7 cm^-1 and 569.7cm^-1, respectively. Beside of this a residual amount of the nitrogen was also found (LVM at 496.3 cm^-1). Electrical parameters versus temperature were measured by Hall method. Optically active deep defects were measured by low temperature photoluminescence (PL) in the spectral range 2eV - 0.7eV. GaP samples of different thickness were also subjected to high temperature annealing from 4 to 88 hours under phosphorous overpressure. After annealing the electrical parameters and PL features were controlled. The results for the samples cut from 6 different GaP crystals were analysed.

The obtained results showed that modification of electrical parameters and luminescence feature can be partly understandable by assuming the creation of a native defect P_Ga (phosphorous atom occupying gallium site place) [2]. The presence of such defect has been confirmed by electron paramagnetic resonance (EPR) in our as grown GaP crystals. However, some of PL features still reminded unclear. During annealing at high temperature the creation of a new electrically active defect was stated. The model of a new defect that allowed us to explain all observed by us modification of electrical parameters has been proposed.

1. D. C. Harris, Infrared Physics and Technology 39, (1998), 185-201.
2. K. Chino, T. Kazuno, K. Satoh, M. Kubota, Semi-Insulating III-V Materials, (1988), 133p.

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1. Making attempts to obtain semiconductor compounds for applications in advanced thermoelectric generators and further investigating
2. Investigation of Ga_1-xIn_xSb crystals growth by Czochralski method
3. Technological conditions to obtain high purity undoped GaP single crystals.
4. Kinetic studies of oxygen related defects in neutron irradiated silicon doped with carbon
5. Stress - mediated solid phase epitaxial re - growth of a-Si at annealing of Si:Mn
6. Diffusion of Mn in gallium arsenide.