Deep centers in AlGaN-based light emitting diode structures

Electrical properties and spectra of deep centers in GaN p-i-n rectifier structures

“…The apparent activation energy for the saturation current in this region was 0.18 eV. This is in good agreement with our earlier measurements on other types of p-i-n structures 16 and suggests that tunneling still remains dominant but the process at play requires some moderate activation of the carriers. For temperatures between 320 K and 400 K the ideality factor continued to slightly decrease (from 1.6 to 1.5) and the apparent activation energy increased to 0.5 eV.…”

“…24 It was also noticed that using p-AlGaN films instead of p-GaN greatly reduces the influence of parasitic Mg diffusion into the undoped i-layer. 16 The densities of deep traps detected in i-layers of type I and type II diodes are not too high per se, but the centers giving rise to persistent changes in conductivity are very undesirable (to say nothing of the defects that can move under applied electric fields at very moderate temperatures not exceeding 120°C as we have demonstrated for our p-i-n structures. 11,12 For type I diodes the electron concentration in the i-layer is too high and the thickness of the layer is too low to allow operation at voltages greatly exceeding 100 V which is confirmed by more detailed studies of the breakdown behavior in such devices.…”

“…(Details of spatial distribution of these two types of behavior and possible relation to the growth process are given elsewhere.) 12,13 Below we treat these two types of structures separately. Figure 1 presents a typical concentration profile derived from C-V measurements at 290 K and 1 MHz on one of the type I diodes.…”

“…This in-diffusion seems to be a quite common feature of GaN-based pi-n structures obtained by standard MOCVD growth. 16,23 It has been suggested, however, that the diffusion is greatly facilitated by the presence of threading dislocations 23 and growth on patterned substrates allowing a decrease in dislocation density might alleviate the problem. 24 It was also noticed that using p-AlGaN films instead of p-GaN greatly reduces the influence of parasitic Mg diffusion into the undoped i-layer.…”

“…The persistent photoconductivity effects for temperatures below room temperature are most likely due to the 0.6 eV electron traps having a barrier for capture of electrons (about 0.15 eV high). 13 The effect at room temperature is due to some unidentified traps. 19 Whatever the reason, one has to be very careful when interpreting the results of I-V and C-V measurements on type II structures lest the above effects alter the results.…”