The deep levels of GaAs

1-

x

P

x

LEDs and their effect on the luminous efficiency are studied by DLTS. The block diagram of apparatus for measuring DLTS is given. The calculating formula about the concentration

depth and capture cross section of deep levels and correlation between the luminous efficiency and minority life time are introduced. Three kinds of GaAs

1-

x

P

x

LEDs with different luminous flux

5.1

0.46

and 1 mlum at 10mA

designated as 1

#

2

#

3

#

LEDS are compared.Their concentration of shallow donor is nearly equal

namely |

ND-NA

| = 2.1~3.1×10

17

cm

-3

.Experi-mental results show that the 1

#

LED with high luminous flux has only one strong and one weak peak located at 0.15 and 0.33eV below the conduction band

no hole deep level is detected. The other LEDs with lower luminous flux have not only more than two electron peaks

but also two hole peaks. The calculated results indicate that it is difficult to ascertain correctly the level depth if there are two kinds of deep level having very close location in the band gap

owing to the emission of electron(or hole) from the levels simultaneously. The parameters of deep levels

luminous flux and others data are listed in Table 1. The luminous efficiencies are proportional to the carrier life-times

qualitatively. The longer the carrier life time

the higher the luminous flux. But larger differences are still discovered by quantitative comparisons of these data

especially for 2

#

LED.For example

ratio of the luminous flux for 1

#

and 3

#

LED is 4.1

the ratio of their life time is~3. But the ratio of the 1

#

flux to that of 2

#

is~10; their ratio of life time is~240.The larger difference in the latter case is probably caused by poor p-n junction preparation resulting in severe leakage current.