Properties of Efficient Silicon-Compensated AlxGa1−xAs Electroluminescent Diodes

Abstract

The properties of p‐n junctions fabricated by Si compensation in the Al_xGa_1−xAs alloy system have been investigated. The radiative emission is shown to occur via centers substantially removed from the band edges. At 300°K, E₀‐hv_p varies from 0.12 eV at a bandgap energy of 1.49 eV to a maximum of 0.33 eV when E₀=1.86 eV. A deep acceptor level due to a Si complex is believed to be involved. As a result internal reabsorption of the emitted light is small compared to Zn‐doped junctions where the emission is closer to the absorption edge. External efficiencies of 1%–2% on uncoated, edge emission diodes are observed in the near‐infrared portion of the spectrum (8600 Å), at current densities as low as 5 A/cm². The highest efficiency obtained is 7% at 8800 Å with an encapsulated diode. The radiative efficiency at 300°K is shown to vary with the bandgap energy (i.e., separation between direct and indirect conduction band minima). For E_g=2 eV (when the indirect band is lower than the direct one by about 0.1 eV), the efficiency is reduced to 0.025% at a peak emission wavelength of 7000 Å. However, at 77°K, the efficiency varies by only a factor of ∼5 between E_g=1.49 eV and E_g=2 eV. The difference between 300° and 77°K is explained by free‐electron‐to‐acceptor‐recombination at 300°K, which changes to donor‐to‐acceptor recombination at 77°K. In comparison with other methods of diode preparation by vapor phase epitaxy or diffusion, (in Al_xGa_1−xAs or GaAs‐P) the present devices offer the convenience of a one step growth process in simple apparatus. The low internal reabsorption further simplifies the diode fabrication process because high efficiency devices are obtained even with edge emission structures. Thus it is possible to have large surfaces available for Ohmic contact which results in minimal diode series resistance.