W. O. Groves

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 ...

The Elastic Constants of Gallium Phosphide

The elastic constants of GaP have been determined by the ultrasonic phase‐comparison method. The frequency range and temperature for the measurements were 8–20 MHz and 300°K, respectively. The compressibility, Debye temperature, and average longitudinal sound velocity in GaP are calculated. The elastic constants of GaP are found to agree with the regularities established from the measurement of these constants in other III–V compounds.

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.

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...

Pulsed room‐temperature operation of In1−xGaxP1−zAsz double heterojunction lasers at high energy (6470 Å, 1.916 eV)

Pulsed room‐temperature operation of LPE In1−xGaxP1−zAsz double heterojunction (DH) laser diodes at short wavelength is described (Jth≲2×104 A/cm2, λ∼6470 A, heterobarrier ΔE∼137 meV). The differential quantum efficiency of these diodes is ηext∼5%, and is considered to be low because of large diode size, thick active region, probably some layer mismatch and growth defects, and relatively poor heat sinking. The temperature dependence of threshold current density (Jth∼J0 expT/T0, T0∼74 °K) is presented in the range 77–300 °K and is compared with similar diodes having smaller heterobarriers and which, as expected, exhibit poorer performance (smaller T0).

Spontaneous and stimulated photoluminescence on nitrogen A‐line and NN‐pair line transitions in GaAs1−x Px : N

In accord with recent absorption measurements, photoluminescence measurements on crystals grown from a Ga solution, as well as on some vapor epitaxial crystals, indicate that the A line in GaAs1−x Px : N is higher in energy than formerly believed. Also, the NN‐pair emission peak (ENN) has been determined more accurately relative to the A‐line peak (EN), and relative to EΓ and Ex. For crystal composition x less than 0.9, only a single NN‐pair emission band is observed with ENN = EΓ at x ≈ 0.30. The A‐line is broad (⩾ 50 A) with EN = EΓ at x ≈ 0.40. For EN ≈ EΓ or ENN ≈ EΓ the recombination probability on transitions involving N traps may be resonantly enhanced. If EΓ is close to or degenerate with EN or ENN, carrier reemission from N traps to the conduction band is fast, and stimulated emission involving N or NN trap centers can lead to line narrowing because the excess electron population can readjust rapidly between trap centers and the Γ conduction band.

Limitations of the direct‐indirect transition on In1−xGaxP1−zAsz heterojunctions

Because In1−xGaxP1−zAsz is the highest‐energy direct‐gap alloy employed in laser diodes, we attempt to establish where the direct‐indirect transition (xc+0.516yc=1.235, 77 °K) hinders or possibly even limits the use of this sytem in large‐barrier (ΔE∼250 meV) double‐heterojunction (DH) structures. The behavior at 300 and 77 °K of the I‐V characteristics of single‐heterojunction and homojunction structures employing high Ga composition (x?0.72, z≲0.01) wide‐gap In1−xGaxP1−zAsz layers, lattice matched on GaAs1−yPy substrates, show that the nature of the direct‐indirect transition of the ternary boundary In1−xGaxP (x∼xc, y=1 or z=0) acts as a limiting factor on the DH diode and laser performance of the quaternary system. As in GaAs1−yPy, donor states associated with subsidiary minima (X) cause a premature onset of the direct‐indirect transition, and limit the growth of lattice‐matched large‐barrier In1−xGaxP1−zAsz (ΔE∼250 meV) DH lasers, with all layers direct, to substrates of composition y≲0.40.

Liquid phase epitaxial In1−x Gax P1−z Asz/GaAs1−y Py quaternary (LPE)‐ternary (VPE) heterojunction lasers (x ∼0.70, z ∼0.01, y ∼0.40; λ < 6300 Å, 77°K)

Laser operation (77°K) of LPE In1−x Gax P1−zAsz/ GaAs1−yPy (x ∼0.70, y ∼0.40, z ∼0.01) heterojunctions is demonstrated at λ<6300 A. The junctions are prepared by the LPE growth of laser‐quality p‐type In1−x Gax P1−zAsz layers on n‐type VPE GaAs1−yPy substrates. It is found that the problem of lattice matching In1−xGaxP on a GaAs1−yPy substrate is eased if the ternary is rendered a quaternary by the incorporation of a small amount of As in the LPE layer. During growth of the resulting p‐type quaternary layer, Zn diffuses into the n‐type ternary substrate, yielding a thin compensated active region. Laser operation of these devices is obtained at significantly shorter wavelengths and lower thresholds than for comparable homojunctions.

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.