用瞬态电容谱法研究GaAs1-xPxLED深能级及其对发光的影响

本文利用瞬态电容潜(DLTS)法测量了不同效率的GaAsxPxLED的深能级浓度、深度、俘获截面.发现效率高LED仅有一个明显的电子深能级△En=0.15eV和一个很弱的△En=0.33eV电子深能级,它们的俘获截面都小于1.5×10-14cm2,总的能级浓度小,约为1.4×1015cm-3.效率差的两只LED一般除有两个以上的电子能级还有两个空穴能级,它们的俘获截面甚至大到2.2×10-12和1.3×10-13cm2;从DLTS图还可以发现谱峰高而宽,说明杂质浓度大,总浓度分别为6.3×1015cm-3和3.4×1015cm-3.讨论了深能级对发光效率的影响.

MEASUREMENT OF THE DEEP LEVEL IN GaAs1-xPxLEDs USING DLTS AND INVESTIGATION OF THEIR EFFECT ON LUMINOUS EFFICIENCY

The deep levels of GaAs1-xPx 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 GaAs1-xPx 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| = 2.1~3.1×1017cm-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.