ИСТИНА

Heterostructures based on polar GaN have the strong intrinsic electric field caused by piezoelectric and spontaneous polarizations due to mismatch of the crystal cells of adjacent heterostructure layers. In present report the internal electric fields in active region of LEDs structures based on multiple InGaN/GaN QWs were investigated by electroreflectance (ER) spectroscopy. The sample under investigation is royal blue LED heterostructure with 5 QWs in active area grown along [0001] direction on sapphire substrate by MOCVD technology. ER spectra were obtained at room temperature in the range of 2.2-3.5eV with different and DC bias voltages. Observed spectra were modified by Kramers–Kronig relations and approximated by sum of Lorenz functions. Obtained dependences of amplitude and peak position from the DC voltage allow us to determinate the inner electric field in different QWs with respect to applied bias voltages. The energies of two QWs showed independence from the external electric field and inner one is 3.0-3.5MV/cm. Other ones showed splitting in energies 75meV with changing the voltage from 0 to -4.5V which corresponds to the difference in electric field 1.8MV/cm. Such behavior of distribution of electric field is connected with the constant influence of external electric field on the two QWs and nonlinear impact on the other ones whereas internal electric field without bias voltage has the contrary dependence from the coordinate in growth direction in active area.