A. H. Herzog

Radiative recombination mechanisms in GaAsP diodes with and without nitrogen doping

The electroluminescent properties of GaAs1−xPx light‐emitting diodes with and without nitrogen doping have been studied at temperatures from 77 to 300 °K. The radiative transitions in the indirect band‐gap region have been identified by a comparison of the emission spectra with those obtained in GaP. At 77 °K nitrogen‐free GaAsP recombination consists of three peaks, shallow donor‐acceptor pair transitions, free‐exciton transitions (which are not observed in pure GaP), and LA phonon‐assisted free‐exciton transitions. As the temperature is increased, the free excitons and/or free electron‐hole transitions become dominant. The indirect energy band gap has been found to exhibit appreciable curvature. The alloy composition at which the direct‐indirect energy band‐gap transition occurs has been found to be xc=0.46 at 77 °K and 0.49 at 300 °K. In nitrogen‐doped GaAsP the 77 °K emission is dominated by transitions associated with nitrogen. For alloy compositions near GaP (x ≥ 0.9) a series of distinct peaks are ...

Electroluminescence of Diffused GaAs1 − xPx Diodes with Low Donor Concentrations

The optical and electrical properties of electroluminescent diodes formed by Zn diffusion into vapor epitaxially grown substrates with donor concentrations in the range 1016–1017 cm−3 have been studied. This doping range, which is somewhat lower than has been previously investigated in the GaAs1−xPx alloy system, has been found to be the optimum range for the fabrication of high efficiency diodes. The spectral emission is appreciably different than has been previously observed. Throughout the alloy composition range at 300° and 77°K a high energy peak occurs within ∼20 meV of the conduction bandedge, and at 77°K a second peak ∼30 meV lower in energy is present. Donor‐acceptor‐pair recombination peaks similar to those observed in GaP, located ∼0.1 and ∼0.37 eV below the bandedge, are found to occur and remain the same distance below the bandedge throughout the indirect region of alloy composition. At 300°K direct recombination from the higher lying k = 0 minimum is observed to persist into the indirect gap...

The Effect of Nitrogen Doping on GaAs1−xPx Electroluminescent Diodes

The efficiency of GaAs1−xPx diodes for x>0.45 has been found to be greatly enhanced by the addition of nitrogen doping. The diodes were fabricated by means of Zn diffusion into vapor‐grown GaAs1−xPx doped with N and Te. The effects of nitrogen doping on diode efficiency, emission spectra, and brightness as a function of alloy composition are discussed.

High‐Efficiency Zn‐Diffused GaAs Electroluminescent Diodes

Electroluminescent GaAs diodes have been fabricated in heavily doped (n > 1018 cm−3) GaAs using ZnAs2 or a Zn–Ga solution as a diffusion source. Using the Zn–Ga source, efficiencies of 1.3–1.4% for planar uncoated devices and 3.2–3.5% with an Epoxy lens are reproducibly obtained, and uncoated devices with efficiencies as high as 1.7% have been observed. A variety of GaAs crystals were evaluated in order to determine the type most suitable for the fabrication of diffused electroluminescent diodes. The optimum material was found to be Si‐doped GaAs with n in the range (2–3) × 1018 cm−3. Both Czochralski and boat‐grown GaAs were investigated. The device efficiency has been found to depend strongly on the etch‐pit density of the crystal, with maximum efficiencies obtained for boat‐grown GaAs with Δ < 103 cm−2. A series of zero dislocation crystals grown using the Czochralski technique was investigated and found to yield lower efficiency devices than boat‐grown GaAs with an etch‐pit density between 102 and 103 cm−2.

Electroluminescence and Electrical Properties of High‐Purity Vapor‐Grown GaP

The electroluminescence, Hall coefficient, and resistivity of high‐purity GaP, grown by means of vaporphase epitaxy on bulk single‐crystal GaP substrates, have been studied as functions of temperature. Hall mobilities as high as 2730 and 189 cm2/V sec have been obtained at 77° and 300°K, respectively. The electroluminescence (EL) of diodes fabricated by Zn diffusion exhibits intrinsic recombination. At 77°K, in addition to the narrow no‐phonon line due to bound exciton recombination at a neutral donor site, the near‐band‐edge EL exhibits a well‐defined series of peaks corresponding to the phonon‐assisted recombination of free excitons. Peaks are observed associated with both the absorption and emission of TA, LA, and TO phonons with energies of 12.5, 31.0, and 44.0 meV, respectively. The intensities of the peaks associated with phonon emission have the approximate ratio 1:3:1.5 for the TO, LA, and TA phonons, respectively. These energies and relative intensities are in good agreement with absorption and c...

Stimulated Emission Involving the Nitrogen Isoelectronic Trap in GaAs1−xPx

Earlier work on III–V semiconductor lasers has shown that stimulated emission occurs on band‐to‐band transitions or via transitions involving donors or acceptors. Based on the behavior of the N isoelectronic trap in promoting efficient carrier recombination in GaP, the present work shows that the N isoelectronic trap in GaAs1−xPx is distinct and over part of the composition range x it can be operated in recombination in the stimulated emission (laser) regime, thus establishing a fundamental new laser transition in a III−V semiconductor. These results (4.2 and 77°K) are obtained by means of optical pumping of lightly doped n‐type samples of estimated high nitrogen concentration.

The luminescent properties of nitrogen doped GaAsP light emitting diodes

The properties of GaAsP:N light emitting diodes, which emit throughout the range from 7000 Å to 5500Å (red to green), have been investigated. The diodes were fabricated by Zn diffusion into n-type vapor phase epitaxial layers doped with nitrogen and tellurium. The emission spectra, luminous efficiency, quantum efficiency, brightness, and decay time constant have been investigated as functions of alloy composition. Also, the luminous output of the devices has been studied as a function of drive current density and temperature. In the yellow and green spectral regions the performance of nitrogen doped diodes is more than an order of magnitude better than that of nitrogen free diodes of equivalent peak emission wavelength. The luminous efficiency of diodes in the redamber spectral region, with alloy compositions near GaAs0.35P0.65 is equivalent to that obtained in GaP:Zn, O red emitting diodes with 2% quantum efficiency.

Quantum efficiency of GaAs electroluminescent diodes

Abstract The external quantum efficiency of tin-doped GaAs diodes in the 1016 to 5 × 1018 cm−3 carrier concentration range was investigated. A maximum efficiency of about 0·18 per cent at 100° K was found at 5 × 1017 cm−3 carriers, when a fixed diode geometry and ZnAs2 junction diffusion at 870° C was employed. The results from a study of the effect of zinc diffusion conditions on efficiency indicate that a substantial increase in efficiency can be obtained by proper control of the zinc concentration gradient near the p−n junction. With the same fixed diode geometry, a quantum efficiency of 0·65 per cent (300° K) was obtained in tin-doped GaAs with a 1·7 × 1018 cm−3 carrier concentration by employing a Zn-Ga alloy diffusion procedure to decrease the surface zinc concentration to less than 1019 cm−3. Capacitance-voltage measurements indicate that this increased efficiency is associated with a linearly graded junction.

Gallium phosphide high‐temperature electroluminescent p‐n‐p‐n switches and controlled rectifiers

Electroluminescent gallium phosphide p‐n‐p‐n switches (dynistors) and controlled rectifiers (thyristors) which are operable in the temperature range 0 ≤ T ≤ 500°C have been fabricated by diffusion of Zn into GaP n‐p‐n structures grown by liquid‐phase epitaxy. Gallium phosphide thyristor forward and reverse blocking voltages as large as 280 and 80 V, respectively, have been observed. These thyristors can be switched to the low‐impedance state by the application of < 5 A/cm2 gate current and exhibit holding current densities of ≈ 15 A/cm2 at a forward voltage of 2.2 V. Forward blocking voltages as large as 380 V at room temperature and 310 V at 415°C have been observed for GaP dynistors. When forward biased into the low‐impedance state, these devices operate as high‐brightness light emitters with room‐temperature emission in the green portion of the spectrum.

Dopant and Alloying Effects in Gamma Irradiated GaAs Light Emitters

Techniques for producing radiation hardening in GaAs light emitters by use of donor dopants and isovalent anion substitutional alloying are reported. Six different donor dopants, within the concentration range from 1 to 20 x 1017 cm-3, were added to GaAs substrates. P-N light emitters were then fabricated and exposed to gamma irradiation from a 60Co source in steps to a total absorbed dose of 108 rads(Si). Results of the study are reported in terms of the damage parameter K¿ ¿¿ where K¿ is the damage coefficient and ¿¿ is the preirradiated minority carrier lifetime. Selenium (Se) was the most effective dopant for hardening GaAs light emitters followed in order of decreasing effectiveness by Sn, Si (donor), Te, Ge (amphoteric), and Si (amphoteric). Two additional observations in this portion of the investigation also seemed to favor the use of Se for hardening: (1) The recovery of the emitters following isochronal annealing occurs in the sequence Se, Sn, Si, Te, and Ge, with the Se-doped samples showing the greatest annealing (to 60% of original quantum efficiency). (2) The shift of the peak emitting wavelength with irradiation (always toward shorter wavelengths) is found to be least for the Se-doped samples. The second technique for hardening involved substituting the isovalent anion phosphorus (P) into the GaAs lattice in place of As. This action resulted in a lowering of the damage coefficient, K¿ , by several orders of magnitude as the P content increased to about 50%.