GaAsP Barriers Research Articles

Physics and characteristics of high performance 1200 nm InGaAs and 1300–1400nm InGaAsN quantum well lasers obtained by metal–organic chemical vapourdeposition

Here we present the physics and device characteristics of high performance strain-compensatedMOCVD-grown 1200 nm InGaAs and 1300–1400 nm InGaAsN quantum well (QW) lasers.Utilizing the GaAsP barriers surrounding the highly strained InGaAsN QW active regions,high performance QW lasers have been realized from 1170 nm up to 1400 nm wavelengthregions. The design of the InGaAsN QW active region utilizes an In content ofapproximately 40%, which requires only approximately 0.5–1% N content to realizeemission wavelengths up to 1300–1410 nm. Threshold current densities of only65–90 A cm−2 were realized for InGaAs QW lasers, with emission wavelengths of 1170–1233 nm.Room temperature threshold and transparency current densities of 210 and75–80 A cm−2, respectively, have been realized for 1300 nm InGaAsN QW lasers. Despite the utilizationof the highly strained InGaAsN QW, multiple-QW lasers have been realized with excellentlasing performance. Methods for extending the lasing emission wavelength up to1400 nm with InGaAsN QW lasers are also presented. Theoretical analysis andexperiments also show suppression of thermionic carrier leakages in InGaAsNQW systems leading to high performance lasers operating at high temperature.

Comparative study of the band-offset ratio of conventionally strained and strain-compensated InGaAs/GaAs QW lasers

In order to achieve good high temperature laser performance, it is essential to have very deep electron wells. InGaAs system on GaAs substrate suffers from poor temperature characteristics due to the electron overflow over the rather small conduction band offset. By means of the Harrison's model, we investigate the effect of the strain compensation on band alignments of InGaAs/GaAs laser system and show that strain compensation improves the band alignments of this laser system. The use of GaAsP or InGaP barrier instead of GaAs barrier results the strain-compensated laser system having better band alignment than that of the conventionally strained InGaAs. Therefore, high temperature operation has been anticipated in these laser systems with strain compensated barriers due to better electron and hole confinement as a result of the increased band offset and a more favorable band offset ratio.

High-performance strain-compensated InGaAs-GaAsP-GaAs (/spl lambda/=1.17 μm) quantum well diode lasers

This letter reports studies on highly strained and strain-compensated InGaAs quantum-well (QW) active diode lasers on GaAs substrates, fabricated by low-temperature (550/spl deg/C) metal-organic chemical vapor deposition (MOCVD) growth. Strain compensation of the (compressively strained) InGaAs QW is investigated by using either InGaP (tensile-strained) cladding layer or GaAsP (tensile-strained) barrier layers. High-performance /spl lambda/=1.165 μm laser emission is achieved from InGaAs-GaAsP strain-compensated QW laser structures, with threshold current densities of 65 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for 1500-μm-cavity devices and transparency current densities of 50 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The use of GaAsP-barrier layers are also shown to significantly improve the internal quantum efficiency of the highly strained InGaAs-active laser structure. As a result, external differential quantum efficiencies of 56% are achieved for 500-μm-cavity length diode lasers.

The effects of interdiffusion on the polarization insensitivity in a tensile-strained barrier GaAs/GaAsP quantum well

The tensile-strained barrier GaAs/GaAsP quantum-well (QW) structure fabricated on GaAs substrate has been used in achieving merged LH and HH valence subbands in order to obtain optical polarization insensitive photonics devices. In this structure, the GaAs QW layer is embedded in tensile-strained GaAsP barriers grown on GaAs substrates. In the case of tensile-strained barrier GaAs/GaAsP QW, a small amount of light-hole (LH) and heavy-hole (HH) splitting is attainable within a large range of well width and P compositions. Through quantum well intermixing, it is possible to cause the coincidence of energy levels of HH and LH resulting in polarization-insensitive device operation. In this paper, the valence HH–LH splitting properties of intermixed GaAs QW with tensile-strained GaAsP barriers are reported.

Temperature-insensitive operation of real index guided 1.06 μm InGaAs/GaAsP strain-compensated single-quantum-well laser diodes

Temperature-insensitive characteristics have been demonstrated in single mode 1.06 μm InGaAs single-quantum-well laser diodes grown by metalorganic vapor phase epitaxy. The large band-gap AlGaInP current blocking layer is employed in the buried-ridge laser structure. Tensile-strained GaAsP barrier layers were used for strain compensation and electron barriers for reducing electron overflow from a quantum well. As a result, almost totally temperature-insensitive light output-current characteristics have been realized. The uncoated device shows the highest record characteristics temperature of 437 K for the threshold current in the range of 20–50 °C. In addition, the slope efficiency does not change over 20–80 °C.

Gain spectra measurement of strained and strain-compensated InGaAsP-AlGaAs laser structures for λ≅800 nm

InGaAsP single quantum wells (QWs) for wavelengths around 800 nm embedded in AlGaAs large optical-cavity waveguide structures are investigated by measuring modal gain spectra and broad-area (BA) laser parameters. The modal net-gain spectra are determined by the variable stripe-length method using current injection. Thick (18 nm) and nearly unstrained QWs show gain spectra without resolved subband structures. The modal gain in TE-polarization is twice as high as in TM-polarization. For thinner (13 nm) compressively strained (0.6%) QWs, the modal gain in TM-polarization and the transparency current density are lowered. For highly strained (1%) QWs, strain compensation by tensily strained GaAsP barriers improves the device performance. BA lasers with 5-nm-thick QWs with strain compensation show a 10% higher differential efficiency in comparison to structures without strain compensation.

High-speed modulation of strain-compensated InGaAs-GaAsP-InGaP multiple-quantum-well lasers

Small signal direct modulation characteristics of InGaAs-GaAsP-InGaP multiple quantum well ridge waveguide lasers (4.5×220 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) are described. The compressive strain of four InGaAs quantum wells is compensated by the tensile strain of GaAsP barriers. The lasers have a threshold current of 8 mA and an internal differential quantum efficiency of 80%. A 3-dB bandwidth of 25 GHz is obtained at 54 mA. It is found that the strain-compensated lasers have a K factor as low as 0.15 ns, implying a maximum 3-dB bandwidth of 59 GHz.

Donor states in Te-Doped GaAs l−xP x

We have investigated the level configuration of the valence subbands in GaAs/GaAs1−xPx (x = 0.23) strained-barrier quantum well structures as a function of the well width. Circularly polarized photoluminescence excitation (CPPLE) spectroscopy was used to identify the heavy- or light-hole character of the optical transitions. Distinct polarization properties were observed in the strain-split heavy- and light-hole bands in the GaAsP barriers, which indicates the photoexcited electrons in the barriers retain spin orientation well even after the capture into the well and the relaxation process. Utilizing this polarization tendency of the transitions in the barriers, we could distinguish unequivocally the heavy- and light-hole character of the quantum well-related transitions. By varying the well width systematically, we observed the level crossing between n = 1 heavy- and light-hole transitions around the well width of 4 nm. This is in good agreement with the calculation based on the effective mass approximation.

Spectroscopic study of beryllium related acceptors in silicon

We have investigated the level configuration of the valence subbands in GaAs/GaAs1−xPx (x = 0.23) strained-barrier quantum well structures as a function of the well width. Circularly polarized photoluminescence excitation (CPPLE) spectroscopy was used to identify the heavy- or light-hole character of the optical transitions. Distinct polarization properties were observed in the strain-split heavy- and light-hole bands in the GaAsP barriers, which indicates the photoexcited electrons in the barriers retain spin orientation well even after the capture into the well and the relaxation process. Utilizing this polarization tendency of the transitions in the barriers, we could distinguish unequivocally the heavy- and light-hole character of the quantum well-related transitions. By varying the well width systematically, we observed the level crossing between n = 1 heavy- and light-hole transitions around the well width of 4 nm. This is in good agreement with the calculation based on the effective mass approximation.

Valence-subband level crossing in GaAs/GaAsP strained-barrier quantum well structures observed by circularly polarized photoluminescence excitation spectroscopy

We have investigated the level configuration of the valence subbands in GaAs/GaAs 1− x P x ( x = 0.23) strained-barrier quantum well structures as a function of the well width. Circularly polarized photoluminescence excitation (CPPLE) spectroscopy was used to identify the heavy- or light-hole character of the optical transitions. Distinct polarization properties were observed in the strain-split heavy- and light-hole bands in the GaAsP barriers, which indicates the photoexcited electrons in the barriers retain spin orientation well even after the capture into the well and the relaxation process. Utilizing this polarization tendency of the transitions in the barriers, we could distinguish unequivocally the heavy- and light-hole character of the quantum well-related transitions. By varying the well width systematically, we observed the level crossing between n = 1 heavy- and light-hole transitions around the well width of 4 nm. This is in good agreement with the calculation based on the effective mass approximation.

Photoluminescence study of (111)-oriented GaAs/GaAsP strained-layer quantum well structure

A GaAs/GaAs1−xPx (x=0.13) strained-layer quantum well structure has been grown on (111)B-oriented GaAs substrate by means of low-pressure (60 Torr) metalorganic vapor phase epitaxy and characterized by photoluminescence (PL) spectroscopy. Despite the partial relaxation of the tensile strain confined in the GaAsP barrier layers, our sample exhibits smooth surface morphology and intense optical emission. Moreover, an evident blue shift of the excitonic transition peak attributed to the screening of the strain-induced internal electric field by the photoexcited carriers, has been observed in the PL measurement.

GaAs/sub 1-x/P/sub x//GaAs quantum-well structures with tensile-strained barriers

An investigation of GaAs QW's with tensile-strained GaAsP barriers grown on GaAs substrates by organometallic vapor phase epitaxy is reported. We demonstrate that this system permits light- and heavy-hole valence bands to be approximately merged within a wide range of well widths and strains, thereby increasing the yield of devices requiring these characteristics. A few series of quantum wells with three phosphorus compositions (6%, 9%, and 19%) were grown and studied by photoluminescence and polarized photoluminescence excitation spectroscopy. We compared our experimentally determined conduction band to heavy-hole and light-hole transition energies with finite potential well calculations utilizing a previously developed strain dependent band offset model. We obtained excellent agreement between experimental and calculated results without any adjustment or fitting of parameters. >

Observation of the valence-subband level crossing in GaAs/GaAsP strained-barrier quantum well structures using circularly polarized photoluminescence excitation spectroscopy

We have investigated the valence-subband level configuration in GaAs/GaAsP strained-barrier quantum wells as a function of the well width. As we systematically varied the well width, we observed the crossover behavior between the n=1 heavy- and light-hole states around the well width of 4 nm. Circularly polarized photoluminescence excitation (CPPLE) spectroscopy was used to identify the heavy- or light-hole character of the observed transitions. Distinct polarization properties were observed in the strain-split heavy- and light-hole states in the GaAsP barriers, which indicated that the photoexcited electrons in the barriers retained spin memory well even after the capture into the well through the relaxation process of energy and momentum. Taking advantage of this method we were able to identify unequivocally the heavy- and light-hole characters of the transitions in the quantum well. The well-width dependence of the intersubband transition energies obtained by the CPPLE measurement is in good agreement with the calculation based on the effective mass approximation.

Pseudomorphic InGaAs-GaAsP quantum well modulators on GaAs

Previous strain-relief p-i-n InGaAs-GaAs quantum well (qw) modulators have incurred surface striations upon growth due to defect formation, resulting in an optically rough surface. We present here a qw modulator on a GaAs substrate with InGaAs wells and GaAsP barriers which balance the strain in the wells so that the lattice does not relax, leading to much fewer defects, and an optically smooth surface. We obtain a transmission change from 60% to 80% at 1014 nm for a sample with a 1 μm thick intrinsic region.