Features of radiative transitions of charge carriers in Al x Ga1−x As and GaAs x P1−x p-n-structures

Abstract

The AlxGa l_xAs and GaAsxPi-x compounds have formed the basis for the development of highly efficient light-emitting diodes for the visible and IR regions of the spectrum. The position of the edge luminescence band in these materials is controlled by the quantity x without a noticeable change in the efficiency of electroluminescence (EL). The losses occurring in this case are caused not only by radiationless transitions of nonequilibrium carriers, but also by rec. mbination in an undesirable spectral regior,. B~I ..... we present results that reveal such a channel of recombination and indicate that under certain conditions its role in the occurring processes can be substantial. We also investigated the EL spectra with reverse-biased diode structures, which indicate the dominant role of hot carriers in the formation of such radiation. The objects of investigation were epitaxial AlxGat-xAs and and GaAsxPl-x p-n structures�9 The layers of AIxGal-xAs of the n- and p-types were obtained by the method of liquid epitaxy on GaAs substrates with a hole concentration of about 1018 cm -3. The width of the forbidden band Eg in the p-type AI0.1sGa0 8sAs layers was 1.66 eV at 300 K, and the hole concentration in it was equal to about 5.1017 cm -3. The n-type AIo4Ga0.6As layers h;ad a large fordidden band (1.95 eV, 300 K), while ~hc electron concentration was close to 2-1018 cm -3. Mesa diodes with an area of 0.4  0.4 = 0.16 mm 2 were formed by chemical etching in a 5H2SO4:2H202:IH2 0 solution at 75-80~ [1 ] using photolithography. Ohmic contacts with both n- and p-regions were created by chemical deposition of Au-Ni-Au with subsequent burning in a flow of dried hydrogen at 420-450~ The lateral and frontal surfaces of the mesa structures were protected by dielectric layers of A1203 and SiOz obtained by pyrolytic deposition in a vacuum chamber. The n-type GaAsxPI-x layers (x = 0.15, Eg = 2.18 eV at 300 K~, which were doped with tellurium up to 1015-1016 cm -3, were obtained by gas-phase epitaxy on n-type GaP substrates with a carrier concentration of 1016-1017 cm -3. The p-n junct,ons were produced by zinc diffusion (to a concentration of 10 )8 cm -3) into an epitaxial n-layer. The use of an Au-Bi (2~o) alloy for ohmic contacts made possible chemical etching of the diodes (in a 3H2SO4:iH202:IHz O solution at 60~ to remove the disturbed laver on the side surface of the p-n-junction after mechanical cutting of the wafer into diodes measuring 0.4  0.4 mm ]2 1. We performed spectral measurements on a setup consisting of a double quartz monochromator with a photomultiplier (1.7-4.0 eV) and a cooled PbS photoresistor r eV) as detectors. The setup was carefully calibrated for spectral sensitivity by a certified tungsten ribbon lamp. Figure 1 presents the spectra of injection EL for the p-n structures under investigation with forward bias. The characteristic feature of these spectra is the presence of wider-band radiation in the IR region (hv < 1.8 eV) along with a dominating shortwave band in the visible spectrum region. As we can see from Fig. 1, the contribution of the IR band to the total radiation of the AlxGa l_xAs p-n heterostructure changes substantially depending on