深能级对GaAs1-xPxLED老化过程的影响

用深能级瞬态谱(DLTS)研究了GaAs1-xPx LED在正向电压,I=100mA(J=250A/cm2)大电流下老化750小时左右的过程中深能级浓度、深度、俘获截面的变化。GaAs1-xPx LED中存在三个电子能级:△En1=(0.19±0.01)eV;△En2=(0.20±0.01)eV;△En3=(0.40±0.01)eV。发现老化之后△En1与△En2的能级密度变小,而△En3的能级宽度却有所增大。同时测量了它们的发光光谱、光通,C-V特性和I-V特性。讨论了深能级在GaAs1-xPx LED老化过程中对发光效率与退化特性的影响。认为△En1与△En2对GaAs1-xPx LED的发光效率与退化特性无影响,而△En3是限制GaAs1-xPx LED发光效率和退化特性的有效复合中心。

EFFECT OF DEEP LEVEL ON DEGRADATION OF GaAs1-xPx LED

The change of concentration, depth and capture cross section of deep level for p+-n GaAs1-xPx LED’s during degradation at large current (J=250A/cm2) for about 750 hours was investigated by DLTS techniques at room temperature, and their luminescence spectra, luminous fluxs and C-V and I-V characteristics were measured. The parameters of deep level before and after degradation are listed in Table 1.It was observed that there were three electron energy levels △En1=0.19±0.01) eV; △En2=(0.20±0.01)eV; △En3=(0.40±0.01)eV] in GaAs1-xPx LED. No new deep level was found after degradation. The luminous efficiency of LED was reduced by 20-35% and then tended to be saturated during aging process, as shown in Fig.3. Experimental results show that the deep energy level density of △En1, △En2 is decreased, while △En3 is increased and its capture cross section is larger. Thereby the △En 1 of capture ration is relatively increased after degradation. As shown in Table 1 the proportion of capture probability of △En3 is increased, although total capture probability of the three energy levels remains almost constant. The capture probability of △En3 is increased by 9,15,26 and 30% respectively and 20% in average for 1#-4# LED’s. Whereas luminous effoiency is decreased about 21%. The results are agreed very well. This means that the decreace of luminous efficiency after degradation is mainly due to △En3 and △En1,△En2 do not influence the luminous efficiency and degradation characteristic at all. Fig.3 shows that the forward threshold voltage and reverse breakdown voltage of GaAs1-xPx LED are decreased after degradation. This means that p-n junction is damaged and the leakage current is increased with degradation. This may be one of the reasons for the reducing of GaAs1-xPx LED luminous efficiency.