AlGaInP Research Articles

High-power red laser diodes grown by MOVPE

We report on the development of high-power laser diodes and laser bars emitting in the visible red spectral region. In contrast to the normally used epitaxial structure consisting of Al(Ga)InP waveguide and cladding layers embedding an GaInP quantum well (QW) we also investigated AlGaAs as material for the cladding layers in a symmetric and in an asymmetric design. The laser performance of the different structures is compared. AlGaAs as p-cladding layer enables the use of carbon instead of zinc as p-dopand resulting in a reduced diffusion tendency of the doping material and a higher possible doping level. Furthermore, the influence of QW number and thickness on the laser performance is investigated. With optimized layer structures 5-mm wide laser bars at 650 nm with a maximal output power of 55 W in pulsed operation were realized.

Theoretical and experimental analysis of current spreading in AlGaInP light emitting diodes

The profile of light emission from aluminum gallium indium phosphide (AlGaInP) light emitting diodes has been studied and compared with the theoretical modeling of current spreading using a lossy transmission line model of current injected into the active region. Discrepancies between the experimentally determined emission profile and the theoretically predicted current injected into the active region have been analyzed and explained using a Monte Carlo ray tracing simulation which considers the trajectories of the photons after leaving the active region and the particular geometry of the device current, die size, and current spreading layer resistance upon the emitted emission profile. The combination of the current spreading and ray tracing models give very good agreement with the experimental emission profiles for both thin and thick current spreading layers.

Effective mass and exciton binding energy in ordered (Al)GaInP quantum wells evaluated by derivative of reflectivity

Low-temperature (1.8 K) magneto-optical reflectivity spectroscopy together with derivative operation has been employed in evaluating the reduced effective mass and exciton binding energy in GaxIn1−xP/AlGaInP quantum wells (QWs). Low uncertainty of the method in identifying excitonic transition energy (⩽0.3 meV) enables a simultaneous determination of both the heavy-hole (hh) and light-hole (lh) excitons in the QWs with ordering. The obtained effective masses manifest to be ordering-dependent, the dependence of which is compared with that reported for the GaInP2 bulk material. Results from the lattice-matched QWs suggest that the magnetic-field enhancement of the oscillator strength is stronger for the hh exciton than for the lh exciton.

Electrical properties of silicon- and beryllium-doped GaInP and (AlGa)InP grown by solid source molecular beam epitaxy

Abstract Silicon- and beryllium-doped Ga0.52In0.48P and (Al0.7Ga0.3)0.52In0.48P were grown by solid source molecular beam epitaxy using a valved phosphorus cracker cell. The electrical properties were investigated using van der Pauw–Hall and capacitance–voltage measurements at room temperature. The highest electron concentration obtained was 6.9×1018 and 2.1×1018 cm−3 for Silicon doped Ga0.52In0.48P and (Al0.7Ga0.3)0.52In0.48P, respectively. The highest hole concentration obtained was 1.1×1019 and 4.9×1018 cm−3 for beryllium-doped Ga0.52In0.48P and (Al0.7-Ga0.3)0.52In0.48P, respectively. The Hall electron mobilities of Si-Ga0.52In0.48P and Si-(Al0.7Ga0.3)0.52In0.48P within the carrier concentration range of 1017

Band structure parameters of quaternary phosphide semiconductoralloys investigated by magneto-optical spectroscopy

The spin-flip Raman scattering by the epitaxial layers ofquaternary aluminium gallium indium phosphide alloys lattice matched togallium arsenide has been investigated in order to gain insight into theband structure parameters of this material system. Both electron and holespin-flip Raman signals were observed and were identified by theirbehaviour on the application of a biaxial strain to the epilayer. Thegyromagnetic ratios of the electron and hole were determined and it wasfound that a three-band k·p model gives a gooddescription of the experimental values of the conduction band gyromagneticratio as a function of composition; these data provide a new insight intothe dependence of the spin-orbit splitting on composition.

Molecular beam epitaxy growth and characterisation of (AlGa)InP using GaP as a phosphorus source

(Al,Ga,In)P is grown by molecular beam epitaxy using gallium phosphide (GaP) as a source of phosphorus. Photoluminescence from the phosphide material is compared to material using phosphine as the phosphorus source. High quality, disordered (Al,Ga,In)P can be grown using GaP, but additional impurities are observed in phosphide material grown by the GaP cell as compared to gas source material.

Point defect reaction in (Al)GaInP STQW lasers enhanced by laser operation

We have found that a large number of dislocation loops of interstitial type are introduced in the active region of (Al)GaInP strained triple quantum wells (STQW) lasers by the effect of laser operation. These loops were always generated in the lasers, the driving current of which increased gradually as operating time increased. We have shown that the dislocation cores act as nonradiative recombination centers and therefore the loops cause the gradual degradation. The migration of interstitial atoms enhanced by laser operation are essential for the degradation of the lasers.

Determination of ordering induced birefringence in (Al)GaInP

In this paper, the first measurement of the ordering induced birefringence in GaInP and (Al0.33Ga0.67)InP is presented. It is found that these ordered crystals are positively birefringent far below the bandgap and become negatively birefringent at the bandgap. The method to measure the birefringence is based on the modifications introduced by ordering to the mode structure of planar waveguides. The change of the sign of birefringence at the bandgap is due to the highly anisotropic interband matrix element. The dispersion of the measured birefringence is in good agreement with six-band k·p calculations.

Transmission electron microscopy observation of lateral order/disorder structures in (Al)GaInP

Ion implantation damaging of ordered (Al)GaInP reduces the temperature threshold for thermal disordering from about 850 °C to temperatures below 800 °C, therefore, annealing at 800 °C leads to selective disordering of implanted regions. Dark-field transmission electron microscopy has been used to study the spatial resolution of implantation-induced disordering of CuPtB-ordered GaInP/AlGaInP heterostructures. Lateral order/disorder structures smaller than 200 nm have been realized using implantation masks defined by electron beam lithography. The lateral extension of disordering observed by transmission electron microscopy is in agreement with photoluminescence data and calculations of the lateral implantation straggling.

Birefringence in ordered (Al)GaInP

We report on a way to examine the birefringence introduced by chemical ordering in (Al)GaInP using waveguide structures. We find that ordered (Al)GaInP is positively birefringent far below the band gap, while approaching the band gap it becomes negatively birefringent. The dispersion of the measured birefringence is compared with calculations that take into account the strongly anisotropic absorption at the band gap due to the splitting of the valence bands. We will show how the polarization state of light traveling along the [011] direction in chemically ordered (Al)GaInP waveguides is affected by the reduced crystal symmetry introduced by ${\mathrm{CuPt}}_{\mathrm{B}}$-type ordering. Birefringence leads to a conversion of transverse electric (TE) and transverse magnetic (TM) polarized light within 60 \ensuremath{\mu}m. This can be understood due to new modes in the waveguide, the ``supermodes,'' with an orientation tilted with respect to the TE/TM orientation. In the [01-bar1] direction, the common TE/TM modes stay unchanged. With a simple theory of mode coupling, it is possible to understand the observed polarization behavior. A transfer-matrix method for anisotropic planar waveguides is used to achieve a more detailed analysis. Consequences and possibilities for applications are considered.

Demonstration of the N2 carrier process for LP-MOVPE of [formula omitted

The suitability of an N2 carrier in LP-MOVPE of GaInAsInP device structures and for the growth of (Al)GaInP is investigated for the first time. Al-free GaInAsInP HEMTs and MSM photodetectors exhibit cutoff frequencies of ft = 135 GHz and fmax = 200 GHz and a bandwidth of 16 GHz and responsivity of 0.27 A/W, respectively. AlGaInP and GaInP layers deposited using the optimized growth conditions showed excellent structural, optical and homogeneity properties. For example X-ray diffractograms with FWHMs as low as 15–16 arcsec for 1 μm thick layers and 300 K photoluminescence mappings over full 2 inch wafers with standard deviations of ±0.23 and ±0.26 nm were obtained for both materials.

Replacement of hydrides by TBAs and TBP for the growth of various III–V materials in production scale MOVPE reactors

Besides the standard group V precursors AsH 3 and PH 3 , so-called alternative precursors like TBAs and TBP (tertiary-butyl-arsine and tertiary-butyl-phosphine) are more and more important in today's MOVPE processes. A lot of publications have demonstrated that these precursors can be successfully used for the growth of different III-V materials. In this study we want to demonstrate that TBAs and TBP can be used as the group V precursor in a complete family of production scale reactors. It is shown that these precursors can be used for the growth of InP-based as well as for GaAs-based materials. The reactors that have been employed are medium scale reactors (AIX 200/4; 1 x 2 inch, 3 or 4 inch or 3 x 2 inch capability) and large scale Planetary Reactors®, in particular the AIX 2400 system (15 X 2 inch or 5 X 4 inch). Materials that have been grown are (Al)GaInP on GaAs and GaInAsP on InP. The lower cracking energy of these precursors compared to PH 3 and AsH 3 allows one to use lower growth temperatures and lower V/III ratios, particularly in combination with the high cracking efficiencies of the used reactors. For the growth of GaInAsP on InP, the consumption of TBP and TBAs is up to 8 times lower than using PH 3 and AsH 3 . GaInP on GaAs could be grown with a V/III ratio as low as 25 in a Planetary Reactor®. Good crystalline quality is demonstrated by DCXD (e.g. for GaInP: FWHM = 35 arcsec, substrate 32 arcsec). PL intensity and growth rate are not affected by using the alternative precursors. The compositional uniformity is similar to layers grown with arsine and phosphine (e.g. 1.5 nm uniformity for GaInAsP (λ = 1.5 μm) on 2 inch; approximately 1 nm uniformity for GaInP) [1,2]. The purity of the grown layers depends mainly on the quality of the TBP and TBAs. Using high purity TBP, InP revealed background carrier concentration in the mid 10 14 cm -3 regime. Our investigation shows that TBP and TBAs can replace phosphine and arsine in state of the art MOVPE reactors. Both for single and multi-wafer production MOVPE reactors these compounds can be used successfully for the growth of the entire material spectrum in the Al-Ga-In-As-P system.

Valence and conduction band-edges-charge densities in Ga 1−xAl xP mixed crystals

The empirical pseudopotential method (EPM) combined with the virtual crystal approximation “VCA” are used to compute electronic charge densities at Γ and X k-points of the valence and conduction band edges in the ternary GaAlP semiconductor alloy. These charge densities are used to study the modifications of the bonding and electronic properties of the alloy with respect to the molar fraction of Al in GaP.

High-quality InGaP and InGaP/InAlP multiple quantum well grown by gas-source molecular beam epitaxy

Using gas-source molecular beam epitaxy, we have obtained high-quality GaInP and (AlGa)InP epilayers lattice-matched to (100) GaAs substrates. All grown layers exhibited mirror-like surfaces. For a 1.7 μm thick Ga 0.5In 0.5P film, the Hall electron mobility was 3400 and 30,000 cm 2 /V·s at 300 and 77 K, respectively. The luminescence wavelength of (Al x Ga 1− x )InP samples ranged from 680 nm (for GaInP) to 590 nm (for AlInP) at room temperature, and from 644 to 513 nm at 77 K. The multiple quantum well (MQW) structure with well width of 40 Å showed strong luminescence intensity with wavelength of 647 nm (300 K) or 622 nm (80 K). The satellite peaks can be detected in double-crystal X-ray (DCXR) diffraction measurements of the MQW samples, which indicates the perfect structural periodicity.

High-resolution electron-beam lithography for fabricating visible semiconductor lasers with curved mirrors and integrated holograms

Abstract Red-emitting (Al)GaInP semiconductor laser diodes with dry-etched mirror facets have been fabricated using chemically assited ion-beam etching. These devices operate single mode up to CW output powers of 30 mW. Their properties are comparable to those of lasers with cleaved mirrors. Additionally, lasers with concave and convex facets have been realized using high-resolution electron-beam lithography to define the mirror shapes. The horizontal far-field behavior of the laser is influenced by varying the shape of the facets. The same technology can be used for integrating computer-generated holograms working as focussing grating couplers.

AlGaInP visible resonant cavity light-emitting diodes

Visible (670-nm) resonant cavity light-emitting diodes (RCLEDs) composed entirely of AlGaInP alloys are discussed. The devices consist of a strained quantum well optical cavity active region surrounded by AlInP/(AlGa)InP distributed Bragg reflectors (DBRs). The bottom DBR is a 60.5 period high reflector while the top partial reflector, which determines the emission linewidth, is a five-period output coupling DBR with a reflectance of about 57%. The devices exhibit linewidths of 4.8 nm (13.3 meV) at 300 K and are promising for plastic fiber communication systems and monochromatic displays. >

Applications of ion implantation in III–V device technology

The use of implantation for doping and isolation of a variety of electronic and photonic III–V compound semiconductor devices will be reviewed. Complex multilayer heterostructure devices like heterojunction bipolar transistors and strained InGaAs-GaAs quantum well lasers rely on keV or MeV isolation implants, requiring thick, easily removed masks and post-implant annealing treatments to achieve high isolation resistances ( ≥ 10 8 Ω cm ). The effectiveness of the implant isolation technique varies as a function of the bandgap and elemental composition of the semiconductor. Devices based on GaAs, Al xGa 1-xAs and InGaP are particularly suited to the implant isolation method. The prime dopant species for III–V materials are Si for n-type layers and Be for p-type layers, although there is increasing interest in the use of C as an acceptor because of its low diffusivity. In the latter case, a group III species must be co-implanted with the C + ion to enhance the occupation of the group V lattice site.

Reliable 1.2W CW red-emitting (Al)GaInP diode laser array with AlGaAs cladding layers

A 1.2W CW AlGaInP/GaInP laser array operating at a wavelength of 690nm is demonstrated. The array consists of 36 lasers on 16 μm centres with 8μ-wide ridge waveguides and has been mounted junction-side down onto a diamond heatsink. Excellent reliability has been proven by lifetime tests at 1.1 W for over 2300 h.

Local mirror temperatures of red-emitting (Al)GaInP quantum-well laser diodes by Raman scattering and reflectance modulation measurements

Temperature rises were measured on cleaved, uncoated mirror facets of junction-side-up mounted (Al)GaInP laser diodes as a function of the injection current by Raman spectroscopy via the Stokes/anti-Stokes phonon line intensity ratio and the phonon line shift as well as by reflectance modulation as a novel application for laser mirror characterization. Below the threshold current the temperature rise is due to Joule heating of the drive current across the ohmic resistor and is ΔT≂35 K at threshold. Above threshold a significant power-dependent heating caused by absorption of laser radiation is superimposed. In this regime the temperature increase is considerably high, i.e., ΔT≥100 K at 4 mW for 5-μm-wide ridge lasers. The different measurement techniques have produced consistent data.

Junction-side up operation of (Al)GaInP lasers with very low threshold currents

Strained (Al)GaInP quantum-well ridge lasers with AlGaAs cladding layers have been fabricated on a 5 degrees -off oriented GaAs substrate. Owing to a heat spreading layer, the devices can be operated junction-side up with a CW threshold current of 13 mA. Singlemode operation is achieved up to power levels of 15 mW for devices with uncoated facets.