Light-emitting diodes are frequently fabricated from homoepitaxial gallium phosphide films doped with nitrogen with an isoelectronic impurity. A convenient way to introduce nitrogen is by use of vapour phase dopant. The nitrogen doping of the p-and n-layer was performed by ammonia vapour. The problem of nitrogen doping in liquid phase epitaxy (LPE) is more complex than in vapour phase epitaxy where nitrogen is incorporated directly at the growth interface.In LPEthe interaction of NH

3

with Ga melt and the diffusion rate of nitrogen in gallium also have to be considered. We have investigated the kinetics process of nitrogen doping in GaP-LPE using NH

3

vapour dopant. The way to measure NH

3

concentration of the carrier gas H

2

was determined by neutralization of a HCl solution of molarity. These investigations have shown that the reaction of NH

3

with Ga is present when ammonia is highly dissociated in GaP-LPE precess. It is known from equation (3) that the GaN concentration in Ga melt is directly proportional to PNH

3

the partial pressure of NH

3

. According to Henry's law:in equilibrium

the concentration of a species within a solid is proportional to the partial pressure of that [species in the surrounding gas. Thus

the nitrogen concentration in GaP-LPE layer is directly proportial to the GaN concentration in gallium melt (i.e. the ammonia partial pressure in hytrogen as expressed in equation(4).Also we have found that nitrogen doping is a kinetics process which is strongly dependent upon the diffusion rate of nitrogen through the growth melt. Using the condition of steady state (

F

1

=

F

2

=

F

3

)

we get the express) ons(8)

(9) for the concentration of the gallium melt-LPE growth interface C

1

and the gas-gallium melt interface C

0

.