Si-doped GaN was grown by MOCVD method using a home-made vertical reactor operating at atmospheric pressure.To prevent parasitic reactions in the gas phase

reagents were mixed at 20mm before reaching the substrate.The growth was carried out on(0001)oriented sapphire substrates using Trimethylgallium(TMGa)and blue-ammonia(NH

3

)as Ga and N sources

respectively.The doping reagents was the diluted silane(SiH

4

).The mixed gases of hydrogen and nitrogen were used as the carrier gases.A thin buffer layer with thickness of about 15um was grown at 520℃ and recrystallized at 1060℃ for 6 minutes.The Sidoped GaN films were grown at 1060℃with the [V]/[Ⅲ]

ratio of 1000: 1 The growth time was an hour with the growth rate in the rage of 1.8-4.0um/h.The photoluminescence(PL)

the Van der Pauw Hall method

and the double-crystal X-ray diffraction(DXRD)were used to measure the optical

electrical

and structural data of these films at room temperature.Table 1 is the characterization data of the Si-doped GaN films.Fig.1 shows the electron carrier concentration and mobility of Si-doped GaN as a function of SiH

4

/TMGa ratio.The carrier concentration varies between 110

17

and 410

19

cm

-3

.The relationship between the carrier concentration and the flow rate ratio of SiH

4

/TMGa is approximately linear.Fig.2 shows the photoluminescence(PL)spectra of Si-doped GaN as a function of the SiH

4

/TMGa ratio at 300K.The excitation-source was a 15mW He-Cd laser.The band-edge emission and deep-level emission were observed around 370um and 550um

respectively.Very strong band-edge emission without yellow band(limited by the apparatus)was observed in Fig.2-D.Fig.3 shows the intensity of band-edge emission

the intensity ratio between band-edge emission and deep-level emission as a function of the carrier concentration of Si-doped GaN films.The intensity of bandedge emission was highly enhanced and the intensity of yellow emission was restrained with the increasing ofcarrier concentration.As shown in Fig.3

Si-doped GaN films

with carrier concentration of 210

19

cm

-3

were obtained.For this kind of film

the intensity of band edge emission is as high as one hundred times of that of unintentional doped GaN and no yellow luminescence can be found.Fig.4 shows the relationships between the SiH

4

/TMGa ratio and the FWHM of double-crystal x-ray diffraction(DXRD)and the growth rate of Si-doped GaN films.The FWHM of DXRD of GaN films became wider when SiH

4

/TMGa ratio increased.However

the growth rate decreased from 4um/h to 1.7um/h with increasing SiH

4

/TMGa ratio.This phenomenon has not been reported to our knowledge.In this paper

Si-doped GaN films with carrier concentration of 210

19

cm

-3

electron mobility of 120.m

2

/V.s can be obtained.FOr this kind of film

FWHM of the band edge emission at room temperature is only 60meV

and no yellow emission can be observed.In this work

the optimum flow ratio of SiH

4

/TMGa was 210

-4

.