A review is presented of the fabrication, operation, and applications of rare-earth-doped GaN electroluminescent devices (ELDs). GaN:RE ELDs emit light due to impact excitation of the rare earth (RE) ions by hot carriers followed by radiative RE relaxation. By appropriately choosing the RE dopant, narrow linewidth emission can be obtained at selected wavelengths from the ultraviolet to the infrared. The deposition of GaN:RE layers is carried out by solid-source molecular beam epitaxy, and a plasma N/sub 2/ source. Growth mechanisms and optimization of the GaN layers for RE emission are discussed based on RE concentration, growth temperature, and V/III ratio. The fabrication processes and electrical models for both dc- and ac-biased devices are discussed, along with techniques for multicolor integration. Visible emission at red, green, and blue wavelengths from GaN doped with Eu, Er, and Tm has led to the development of flat-panel display (FPD) devices. The brightness characteristics of thick dielectric EL (TDEL) display devices are reviewed as a function of bias, frequency, and time. High contrast TDEL devices using a black dielectric are presented. The fabrication and operation of FPD prototypes are described. Infrared emission at 1.5 /spl mu/m from GaN:Er ELDs has been applied to optical telecommunications devices. The fabrication of GaN channel waveguides by inductively coupled plasma etching is also reviewed, along with waveguide optical characterization.

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Rare-earth-doped GaN: growth, properties, and fabrication of electroluminescent devices

Visible and infrared (IR) rare-earth-activated light emission has been obtained from Er-doped GaN electroluminescent devices (ELD). The ELD consists of an in-situ Er-doped GaN layer grown on either a sapphire or silicon (Si) substrate. The temperature dependence of the light emission and the current conduction is reported. The EL spectrum shows two main visible peaks at 537 and 558 nm and a group of closely spaced IR peaks clustered around 1550 nm. The 558 nm visible transition is dominant below 250 K, whereas the 537 nm transition is dominant at higher temperature peaking at 300 K. Temperatures from 240-500 K have minimal effect on IR emission intensity. A simple model consisting of two back-to-back Schottky diodes explains the current-voltage dependence. The effect of Er doping and substrate type on carrier transport is investigated as a function of voltage and temperature. Specifically, there is evidence that an Er-related defect is responsible for carrier generation at temperatures above 300 K. The effect of bias polarity on spatial confinement of the light emission in different areas of the devices is discussed. The model indicates that both electric field intensity and current density are important in producing light emission. The model also accounts for the uniformity of the emission under the electrodes when considering the type of substrate used for GaN:Er device growth.

Temperature behavior of visible and infrared electroluminescent devices fabricated on erbium-doped GaN

The temperature dependencies of the current–voltage characteristics and the electroluminescence (EL) intensity of molecular beam epitaxy grown Er/O-doped Si light emitting diodes at reverse bias have been studied. To minimize the scattering of electrons injected from the p-doped Si1−xGex electron emitters, an intrinsic Si layer was used in the depletion region. For many diodes, there is a temperature range where the EL intensity increases with temperature. Data are reported for a structure that shows increasing intensity up to 100 °C. This is attributed to an increasing fraction of the pumping current being due to phonon-assisted tunneling, which gives a higher saturation intensity, compared to ionization-dominated breakdown at lower temperatures.

Origin of abnormal temperature dependence of electroluminescence from Er/O-doped Si diodes

In p–n junctions based on c-Si:Er, we have observed strongly efficient excitation of erbium electroluminescence at 1.54 μm. Excitation of erbium ions is accompanied by strong recombination of free carriers indicating a participation of an Auger mechanism. A possible excitation mechanism is proposed which is the Auger recombination of electrons occupying the upper subband of the conduction band with free holes in the valence band, whereas the energy of the recombination process is transferred by Coulomb interaction to 4f electrons of an erbium ion transmitting it to the second excited state 4I11/2 (excitation energy 1.26 eV). The observed three-level excitation of erbium ions is promising for the development of a Si:Er laser.

Efficient Auger-excitation of erbium electroluminescence in reversely-biased silicon structures

Erbium-doped layers have been produced on 〈1 1 1〉 -oriented silicon wafers using high-energy amorphizing Er implants and solid phase epitaxy (SPE). Transmission electron microscopy (TEM) and X-ray diffraction (XRD) techniques, used to study the microstructure of these layers, revealed the presence of microtwins and dislocations. The twins were found to be platelets with lateral dimensions of 15–30 nm and a thickness of about 2–9 nm, and their density throughout the regrown layer was nonuniform. The dislocation densities observed in the regrown layers were very high with densities exceeding 1010 cm−2. Within the implant fluence range studied, between 1×1014 and 9×1014 Er cm−2, the twin and dislocation densities were observed to increase with fluence, while the twin dimensions were found to decrease.

Defect structure of erbium-doped silicon layers formed by solid phase epitaxy

Electroluminescence (EL) and electrophysical characteristics of erbium and oxygen coimplanted and annealed p–n junctions, characterized by higher values of the Er3+-related EL intensity at ∼1.54 μm in the breakdown regime at 300 K as compared with that at 85 K, have been studied in the temperature range from 85 to 300 K. Hole traps in the Er–O codoped n layer were found to be responsible for the anomalous EL behavior. Er-related EL was observed in the same samples in avalanche breakdown at high temperatures and in tunnel breakdown at low temperatures.

A. N. Yakimenko

Papers

Anomalous temperature dependence of erbium-related electroluminescence in reverse biased silicon p-n junction