Study on the luminescence of GaP:N under selective excitation of excitons bound to NN1 centers

Journal of Luminescence 40&41 (1988) 525—526 North-Holland, Amsterdam

525

STUDY ON THE LUMINESCE!’~CEOF Gal’: N UNDER SELEETIVE EXCITATION OF EXCI~1ONSBOUND ~IONN

1

Qiang HONG, Kai LOU and Xinyi ZH1~NG Changchun Institute of Physics, Academia Sinica, Changchun, P - R. China Under selective excitation of excitons bound to NN centers, we observed and studied the luminescence of excitons bound to shallower NN. (i=3, 4, ~), isolated nitrogen centers and of free excitons. 1 1. The INTROLUCTION photoluminescence of excitons bound to

7 W/a-n2 at the focus point reach as high as 3x10 of lens. The pulse tenporal width is about 7 ns

isoelectronic

and the pulse repetition frequency is 15 Hz. The

traps in Gap: N has been studied

for many years. ?.bst of the properties of van-

GaP:N sanple was grown by liquid phase epitaxy

ous NN. centers are well known now’

mathod whose nitrogen concentration was about

To our

knowledge, in all the previous works the excita-

6x1017 an~3. The sanple was placed in a cryo-

tion photon energies are higher than the ~m~_

genic system, the sanple tenperature can be

sion photon energies.

changed from 8 K to 300 K. The emission light of

As there exist nonradiative decay, Auger

sanple was collected into a SPEX double grating

effect and tunneling of the whole exciton to

nonochromstor, detected by a photonultiplier and

another centers other than the radiative pro-

through a Boxcar averager the signal was inputed

the possibility turning to shallower ble

-

of deeper bound excitons

to digital

bound exciton is reasons-

microprocessor.

At 8 K, tuning the wavenurrber of dye laser to

And if the excitation density is high

17857 crn~ (about the energy of an exciton bound

enough, the phenonEnon should be observable3,

to NN 1 plus the energy of a LA phonon of GaP: N),

At low ten-perature,

under selective

excita-

under high density excitation,

tion of excitons bound to NN1 centers, we observed the luminescence of excitons bound to ~

we have maasured

the luminescence of excitons bound to NN1 and -

its phonon replica and that of excitons bound to

(i=3, 4, 5), isolated nitrogen and of free exci-

NN3, NN4, MN5, isolated nitrogen and of free

tons at the high energy side of exciting laser. We propose effect that this phenomanon is with due to the tunneling of bound excitons the

excitons, as shown1.in Its the energy figure.is The position about 12 neV of FE is 18784 cm higher than that of excitons bound to isolated

assistance of phonon annihilation or Auger effect. We have also done the luminescence dynam-

nitrogen. We treasured the luminescence intensity as a

ins analysis on the experlirental

function of sanple tenperature. The teilperature was changed from 10 K to 100 K. Because the band

results.

2. EXPERIMENT We have used a Nd:YAG punped tunable dye

gap of GaP:N will change as sairple tenperature is raised, we slightly changed t1~ exciting

laser whose wavenuirber range is from 17640 to

laser wavenunter for different tenperature to

18050 cm’ - The dye laser power density ~

tfl5tch the varistion of band gap. The excitation

*

Project supported by the Science Fund of the Chinese Academy of Sciences

0022—2313/88/$03.50 © Elsevier Science Publishers BV. (North-Holland Physics Publishing Division)

Q. Hong et a!. / Study on the

526

~NN

3

/ ~

luminescence of GaP.N

tation condition. While the selective excitation density is so high that the density of excitons

N

MN4

~

MN l810~ / 17700

17000

NN1 bound to MN1 is close the interaction to the between concentration bound exciof tons centers, and lattice and between bound excitons becone v~ strong. ~ these ~ the exciton

18800 WAVENUMBER (cm’)

tunneling effect obvious. The dependence of the intensity of the lumi-

FIGURE Luminescence spectra of GaP: N. The excitation 7 W/cm2 wavenurrber is 17857 and excitation density is 2x10

nescence of MN1 on tenperature in our expeninent was different from that under weak excitation condition. This difference is easy to be understood considering that the tine spent to reach

density was 2xl07 W/cm2. The luminescence of

thenrel equilibrium of excitons population and

MN 4, NN5 decreased as the tenperature rose,

the tine of tunneling process are rruch shorter

similar to their behaviours under band gap exci-

than the tine every excitation pulse lasts

tation condition.

ns) while the excitation density was very high.

From 20 K to 100 K, the

(7

nescence of MN3 decreased. The luminescence intensity of MN1 changed only a little and the

t~

FWHM increased obviously from 5 W/ 2 10 K to 100 K. At 8 K, from 2.4x10 cm we increased excitation density about 100 tines graduallythe to

strong high density excitation, the population under of excitons bound to MN than that of excitons bound to 3 MN can be ~. So larger the lumi-

measure the intensity of the luminescence of

nescence of MN

5 to 8x105 both MN and MN centers. From 2. 4x10 21 3 W/cm , there was only the luminescence of MN1

3 will be stronger and increase faster than that of MN 1 from a particular exci-

and its phonon replica increasing with W/cm2, the 5 to 4x106 excitation density. From 8x10 the luminescence of MN

the density that saturates the MN1 centers.

3 appeared and increased faster than that of MN1 did, but the intensity 6 of MN3 was weaker than that of MN1 From 4x10 to 2xl07 W/cm2, the luminescence of- MN 3 increas-

Because the nuither of MN3 pairs is larger that of NM1 and the tunneling effect is

tation density. The particular

density may be

We acknowledge Dr. Li Guiying for supplying the samples used and thank our colleagues for helpful discussions.

ed faster and its intensity became stronger than the intensity of MN1, as shown7 inW/cm2. the figure for the excitation density of 2x10

1. D.M. Roessler and D.E. Swets, J. Appl. Phys.

3. ANALYSIS

2. M.D. Sturge et al., Phys. Rev. Bl5 (1977) 3169.

49 (1978) 804.

The experimental results suggest that the tunneling effect of the whole exciton bound to

~

P. J. Wiesner et al., Phys. Rev. Lett. 35

MN 1 can be very strong under high density exci-

(1975) 1366.