Growth Of GaInNAs Research Articles

High-Quality Growth of GaInNAs for Application to Near-Infrared Laser Diodes

GaInNAs was proposed and created in 1995. It can be grown pseudomorphically on a GaAs substrate and is a light-emitting material with a bandgap energy that corresponds to near infrared. By combining GaInNAs with GaAs, an ideal band lineup for laser-diode application is achieved. This paper presents the reproducible growth of high-quality GaInNAs by molecular beam epitaxy. Examining the effect of nitrogen introduction and its correlation with impurity incorporation, we find that Al is unintentionally incorporated into the epitaxial layer even though the Al cell shutter is closed, followed by the concomitant incorporation of O and C. A gas-phase-scattering model can explain this phenomenon, suggesting that a large amount of N2 gas causes the scattering of residual Al atoms with occasional collisions resulting in the atoms being directed toward the substrate. Hence, the reduction of the sublimated Al beam during the growth period can suppress the incorporation of unintentional impurities, resulting in a highly pure epitaxial layer.

Microelectrical characterizations of junctions in solar cell devices by scanning Kelvin probe force microscopy

Scanning Kelvin probe force microscopy was applied to the microelectrical characterizations of junctions in solar cell devices. Surface Fermi-level pinning effects on the surface potential measurement were avoided by applying a bias voltage ( V b ) to the device and taking the V b -induced potential and electric field changes. Two characterizations are presented: the first is a direct measurement of Bi-induced junction shift in GaInNAs(Bi) cells; the second is a junction-uniformity measurement in a-Si:H devices. In the first characterization, using Bi as a surfactant during the molecular beam epitaxy growth of GaInNAs(Bi) makes the epitaxial layer smoother. However, the electrical potential measurement exhibits a clear Bi-induced junction shift to the back side of the absorber layer, which results in significant device degradation. In the second characterization, the potential measurement reveals highly non-uniform electric field distributions across the n–i–p junction of a-Si:H devices; the electric field concentrates much more at both n /i and i /p interfaces than in the middle of the i-layer. This non-uniform electric field is due possibly to high defect concentrations at the interfaces. The potential measurements further showed a significant improvement in the electric field uniformity by depositing buffer layers at the interfaces, and this indeed improved the device performance.

Growth of GaInNAs and 1.3 μm edge emitting lasers by molecular beam epitaxy

We show that the use of a low growth rate combined with low N flux and RF power during molecular beam epitaxy (MBE) growth of dilute nitrides can efficiently enhance N incorporation while retaining good optical quality. A maximum light emission wavelength of 1.44 and 1.71 μm has been obtained at 300 K from GaNAs and GaInNAs quantum wells, respectively. We demonstrate high-performance 1.3 μm GaInNAs multiple quantum well edge emitting lasers with record low threshold current densities, a 3 dB modulation bandwidth of 17 GHz at 300 K and capability of being modulated at 10 Gbit/s up to 110 °C without extra coolers. Our results show that MBE is an epitaxial technology suitable for the growth of dilute nitride materials and devices.

Dilute nitrides and 1.3 μm GaInNAs quantum well lasers on GaAs

We present epitaxial growth of GaInNAs on GaAs by molecular beam epitaxy (MBE) using analog, digital and N irradiation methods. It is possible to realize GaInNAs quantum wells (QWs) with a maximum substitutional N concentration up to 6% and a strong light emission up to 1.71μm at 300K. High quality 1.3μm GaInNAs multiple QW edge emitting laser diodes have been demonstrated. The threshold current density (for a cavity of 100×1000μm2) is 300, 300, 400 and 940A/cm2 for single, double, triple and quadruple QW lasers, respectively. The maximum 3dB bandwidth reaches 17GHz and high-speed transmission at 10Gb/s up to 110°C under a constant voltage has been demonstrated.

Preface: phys. stat. sol. (c) 5/2

AbstractThis issue of physica status solidi contains a collection of contributions of Symposium F of the 2007 Spring Meeting of the European Materials Society (E‐MRS) entitled “Novel Gain Materials and Devices Based on III–N–V Compounds”, held in Strasbourg (France) on 30 May–1 June 2007. This two‐day symposium had a busy schedule containing 6 invited, 39 oral and 28 poster presentations. Also, three students, Paul Jefferson, Miguel Montes Bajo, and Giorgio Pettinari were awarded the Graduate Student Award by the Organizing Committee and one student James Chamings, was awarded the Best Poster Prize.The research presented in the symposium reflected the current state‐of‐the‐art in the novel semiconductor III–N–V compounds including GaInNAs, GaNP, GaInPAs, GaN, GaInN and with special emphasis given to InN, comprising both material and device aspects. The symposium started with a session on short wavelength nitrides through an excellent invited talk on the recent modelling and test results, showing successful optimization of optical InGaN‐based devices emitting in the wavelength range 420–650 nm. Several talks focused on the MBE and MOVPE growth of these materials and two talks on transport devices: one on high power and one on bistability. The following session was on the novel GaNAs, GaAsNP, and GaInNP materials systems just being started to be explored where basic material properties and quantum well (single and multiple) structures were reported on. An exhaustive invited talk on the effective mass in GaAsN was also presented. This was followed by a session on the InN material system which has attracted substantial interest as its bandgap has been found to be 0.7 eV. An introductory talk gave an extremely clear overview of this very interesting system. Material issues of doping and interfaces were reported in this very growth orientated session. The following two sessions were chiefly devoted to the well‐studied and comparably mature system GaInNAs, although some new variants were also presented. Results of growth of GaInNAs on both GaAs and InP as well as very basic and application‐focused work was presented. This part of the symposium also contained an excellent overview of recent studies of InGaAsN/InP lasers and the novel GaInNP/GaAs system. The next session focused on devices based on dilute nitride materials which started with an excellent overview on optoelectronic devices based on GaInNAs, particularly VCSEL and VECSEL‐based applications. The potential for disc lasers, amplifiers, VECSELs and VCSELs was further explored in this session. The final session was on electronic devices where oxide interface studies as well as electrical and optical studies were featured. This highlight may illustrate the broad scope of the symposium which, as we hope, will contribute to the further proliferation of this field.Finally, we would like to thank the invited speakers for their high level presentations, the authors, and all participants for their valuable contributions, as well as the referees for their efforts and the Wiley‐VCH staff. We express to all our deep gratitude.Symposium F Organizers

Dilute nitride GaInNAs and GaInNAsSb solar cells by molecular beam epitaxy

Dilute nitride films with a roughly 1 eV band gap can be lattice-matched to gallium arsenide and germanium, and therefore could become a critical component in next-generation multijunction solar cells. To date most dilute nitride solar cells have been plagued with poor efficiency, due in large part to short diffusion lengths. This study focuses on two techniques aimed at improving the quality of dilute nitride films grown by molecular beam epitaxy: the utilization of biased deflection plates installed in front of the nitrogen plasma source, and the introduction of antimony during growth. Results from GaInNAs cells grown with and without deflection plates, and GaInNAsSb solar cells are reported. The use of biased deflection plates during GaInNAs growth improved every aspect of solar cell performance. For the GaInNAs devices grown with deflection plates, the dark current density, open-circuit voltage, and fill factor were the best of the devices studied. The GaInNAsSb cells had the highest quantum efficiency, almost 80% at maximum, mainly due to low background doping densities providing these devices with wide depletion widths. The GaInNAsSb materials also had quite narrow band gaps of 0.92 eV. Because of the high collection efficiency coupled with the narrow band gap, the sub-GaAs short-circuit current density produced by the GaInNAsSb cells is 14.8 mA∕cm2, which was the highest of the devices studied. This current is nearly 50% greater than the best dilute nitride solar cells in the literature, and is the first dilute nitride cell to produce enough current to current match the upper two subcells in a triple-junction device, composed of GaInP/InGaAs/GaInNAsSb.

Evaluation of incorporation efficiency of group V source gases in metal organic chemical vapor deposition of GaInNAs for high quality 1.21 μm quantum-well ridge wave guide lasers

For the growth of GaAs and AlGaAs by metalorganic chemical vapor deposition (MOCVD), the residual carrier concentration was confirmed to follow the relation of [Carrier concentration] ∝ [V/III] −4/3. As this relation fit various growth conditions, it provided a basis for a new parameter of “effective TBAs concentration” which represents the concentration of the tertiarybutylarsine (TBAs) effectively contributing to the growth of epitaxial layer. By using this new parameter, a large spatial variation of the efficiency of TBAs across a wafer in a direction of the gas flow was indicated for the growth of Ga(Al)As at low temperature of 500 °C. With using this parameter, the decomposition of 1,1-dimethylhydrazin (DMHy) was suggested to occur only on the wafer at this temperature. The optimized TBAs flow rate for the growth of GaInNAs deduced by considering the distribution of the effective TBAs concentration coincided with the optimized actual input TBAs flow rate. This coincidence supported the appropriateness of the method of measuring the efficiency of TBAs on the wafer with the effective TBAs concentration. The optimized TBAs flow rate obtained by using the new parameter was applied to the growth of a GaInNAs quantum well (QW) and to the fabrication of a high quality laser diode emitting at 1.21 μm.

Low-acceptor-concentration GaInNAs grown by molecular-beam epitaxy for high-current p-i-n solar cell applications

We report GaInNAs grown by solid-source molecular-beam epitaxy (MBE) with background acceptor concentrations less than 1014cm−3, yielding depletion widths in excess of 3μm. GaInNAs p-i-n solar cells fabricated from this low-acceptor-concentration material show greatly increased photocurrents and internal quantum efficiencies close to unity for band gaps as low as 1.15eV. The low acceptor concentrations may be due to low levels of background impurities, such as hydrogen and carbon, in the MBE-grown layers. We discuss the dependence of the acceptor concentration on the substrate temperature used for GaInNAs growth.

Influence of lattice‐matching on structural properties of GaInNAs epitaxial films grown on GaAs

We studied the relationship between lattice-matching and crystalline quality of GaInNAs films grown on GaAs(001) substrates. The lattice mismatch between GaInNAs and GaAs was varied from –0.35% to 0.29%, and the coherent growth of GaInNAs for all of sample in this study was confirmed by (224) X-ray reciprocal space mapping. The full-width at half-maximum (FWHM) of (004) rocking curves showed minimum at the lattice-matched condition, and the FWHM did not depend on N composition. In Raman scattering measurements with the spectrum range of nitrogen-related local-vibrational mode (Ga-N like LO2 mode), a broad peak at 470 cm–1 was observed for all of GaInNAs samples. In addition to the peak at 470 cm–1, a clear shoulder peak at 490 cm–1 which has been understood as stress-relaxation mode was observed only at the lattice-matched sample. It was found that the lattice-matching has a significant effects not only on the crystal axis orientation but also local stress relaxation. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Critical RF damage conditions for the plasma-assisted molecular beam epitaxy growth of GaInNAs with dilute N 2/Ar gas mix

In this work, we investigate the operating conditions for RF plasma sources that employ nitrogen–argon gas mixtures for the molecular beam epitaxy growth of dilute nitride, narrow-bandgap semiconductors. The effects of RF power and gas flow rate variations are discussed, wherein a ‘critical’ RF power level is identified at 300 W. Growths performed at RF powers below this critical setting resulted in noticeably better quality material, which was determined from a comparison of pre- and post-anneal room temperature photoluminescence measurements. In addition to the RF power, the gas flow rate directly influences the growth chamber pressure, which in turn also affects the material quality. A modified pumping configuration was used to decouple the chamber pressure from the gas flow rate. In all growths, lower chamber pressures resulted in better material quality, irregardless of the power setting used. These results suggest that operating the nitrogen RF plasma source at its lowest possible power setting and lowest gas flow rate, while still maintaining a stable plasma, will result in the best quality of dilute nitride materials.

Nitrogen plasma optimization for high-quality dilute nitrides

Growth of GaInNAs by molecular beam epitaxy (MBE) generally requires a nitrogen plasma, which complicates growth and can damage the wafer surface. Optical spectra from both ends of the plasma cell were nearly identical, and were found to be insensitive to certain changes in the cell condition evidenced by a change in reflected RF power and stability. A slight amount of excess capacitance in the matching network improved stability, particularly while the cell warmed up. Furthermore, despite steps to reduce the ion flux from the plasma, a remote Langmuir probe showed significant ions. Moderate voltages on deflection plates were sufficient to remove these ions, with a 3– 5 × increase in photoluminescence resulting from 18–40 V deflection.

Growth of GaInNAs by atomic hydrogen-assisted RF-MBE

We investigated the effect of atomic H irradiation on thin-film growth of GaInNAs by hydrogen-assisted RF-molecular beam epitaxy (RF-MBE) from the viewpoint of growth dynamics and crystal quality. The crystal quality of GaInNAs was characterized by X-ray diffraction and photoluminescence (PL), and the surface morphology was characterized by using atomic force microscope. The atomic H irradiation during the growth of GaInNAs in RF-MBE was found to be effective in improving the overall quality of the epilayers. Further, it was found that atomic H irradiation has an effect of suppressing the three-dimensional growth thereby promoting a two-dimensional growth as well as is effective in passivating the defects and suppressing the recombination from localized states. Low temperature (77 K) PL measurements showed that the incorporation of N into InGaAs effectively reduces the emission energy. An emission enhancement in GaInNAs grown with atomic H was observed at 1.2 μm.

Effect of In and N incorporation on the properties of lattice-matched GaInNAs/GaAs grown by radio frequency plasma-assisted solid-source molecular beam epitaxy

We present the effect of nitrogen (N) and indium (In) incorporation on the structural and optical properties of Ga1−xInxNyAs1−y with low lattice mismatch to GaAs grown by solid-source molecular beam epitaxy using a radio frequency (rf) nitrogen plasma source. The results show that excessive introduction of nitrogen during the growth of GaInNAs may lead to greater incorporation of interstitial nitrogen and degradation in crystal quality. This effect is more significant in GaInNAs compared to GaNAs. A drastic 6× increase in x-ray diffraction full width at half maximum (XRD-FWHM) was observed in GaInNAs compared to 1.5× increase of the same in GaNAs when reactive nitrogen is introduced into the material. The more significant degradation in GaInNAs quality is believed to be due to greater incorporation of interstitial nitrogen in the presence of indium during growth. By changing the In content and fixing the N incorporation rate, a sample of Ga0.924In0.076N0.026As0.974/GaAs with relatively low lattice mismatch of −896 ppm (or ∼8.96×10−4) was grown. Low temperature (4 K) photoluminescence emission at 1518 nm was observed and XRD-FWHM of 118.2 arcsec was measured.

RF-MBE growth and Raman scattering characterization of lattice-matched GaInNAs on GaAs(0 0 1) substrates

RF-MBE growth of GaInNAs systems on GaAs(0 0 1) substrates and Raman characterizations of the local structures of the grown layers have been investigated. Indium beam irradiation during the GaInNAs growth has a strong influence on the nitrogen incorporation to the grown layers. Raman scattering measurements have revealed that the formation of ordered domains such as (GaN)(GaAs) natural superlattice cluster in the GaInNAs layers is suppressed by the In incorporation.

Kinetic modeling of N incorporation in GaInNAs growth by plasma-assisted molecular-beam epitaxy

We have studied the growth of GaInNAs by a plasma-assisted molecular-beam epitaxy (MBE). It was found that the N-radicals were incorporated into the epitaxial layer like dopant atoms. In the range of 400–500 °C, the growth temperature (Tg) mainly affected the crystal quality of GaInNAs rather than the N concentration. The N concentration dropped rapidly when Tg exceeded 500 °C. Considering N desorption alone is insufficient to account for the strong falloff of the N concentration with Tg over 500 °C, the effect of thermally-activated N surface segregation must be taken into account. The N concentration was independent of the arsenic pressure and the In concentration in GaInNAs layers, but inversely proportional to the growth rate. Based on the experimental results, a kinetic model including N desorption and surface segregation was developed to analyze quantitatively the N incorporation in MBE growth.

CBE and MOCVD growth of GaInNAs

We have investigated growth of GaInNAs by MOCVD using dimethylhydrazine (DMHy) and by CBE using RF-radical nitrogen. It was found that there was a large difference in nitrogen incorporation characteristics between the two growth methods. Nitrogen composition of MOCVD increased with a superlinear characteristic against nitrogen source flow and indium composition enhanced such a characteristic. CBE showed a linear incorporation characteristic of nitrogen composition due to the strong reactivity of nitrogen atoms. Photoluminescence intensity was decreased by increasing emission wavelength for both growth techniques, however, the degradation behavior seemed to depend on the nitrogen incorporation characteristic. The hydrogen and carbon concentration of MOCVD grown sample was more than ten times larger than that of CBE grown samples. The comparison of growth characteristics and material qualities may provide useful information for improving the GaInNAs crystal quality.

Growth of GaInNAs by Plasma Assisted Molecular Beam Epitaxy

ABSTRACTThe nitrogen containing alloy GaInNAs has attracted a great deal of interest recently for optoelectronic device applications at long wavelengths, especially 1.3µm, on GaAs substrates. What has been observed is that the material quality degrades rapidly with the addition of nitrogen. In this work we systematically explore the parameter space for the growth of GainNAs using plasma-assisted MBE and inert gas dilution. Inert gas dilution allows additional control of the production of active nitrogen; thus we can independently adjust RF power, gas flow rate, and nitrogen generation, which is used to study the effects of the plasma on the growth surface. In addition to examining the effects of plasma operating conditions, we will also explore the effects of other growth parameters (arsenic to nitrogen ratio and growth temperature) on the resultant structural and optical properties. These properties will be explored by photoluminescence, SIMS, and x-ray diffraction with the goal of understanding how nitrogen incorporation affects the resultant material properties. The resulting information is used to grow high quality layers for GaNAs avalanche photodiodes with a cut-off wavelength of 1.064µm

Comparison of hydrazine, dimethylhydrazine, and t-butylamine nitrogen sources for MOVPE growth of GaInNAs for solar cells

Dimethylhydrazine (DMHy) has been shown to be an effective nitrogen source for the growth of the alloy Ga 1− x In x N y As 1− y (x, y⪡1) . However, high DMHy flow rates are required, and low diffusion lengths and high p-type background doping concentration are typically observed in the grown material. It is therefore of interest to evaluate alternative nitrogen sources. Here, we evaluate two such sources: hydrazine and tertiarybutylamine. Hydrazine is of particular interest because it contains no carbon, suggesting that it might yield lower p-type background doping than DMHy does. With tertiarybutylamine, no nitrogen incorporation was observed, even with nitrogen/III ratios as high as 2000, and so does not appear promising. With hydrazine, by contrast, significant nitrogen incorporation was observed, even at much lower nitrogen/III ratios than would be required using DMHy. However, the p-type background doping appears no lower than with DMHy.

Nitrogen incorporation rate, optimal growth temperature, and AsH 3-flow rate in GaInNAs growth by gas-source MBE using N-radicals as an N-source

We have investigated the conditions for growing GaInNAs by gas-source MBE using N-radicals as an N-source. The optimal growth temperature of GaInNAs with good surface morphology and PL characteristics was clarified: at higher growth temperature, the surface morphology degraded. On the other hand, PL intensity became weak at temperatures lower than the optimal one. This trend is similar to that in GaInAs grown by MBE. AsH 3-flow rate mainly affected crystal quality of GaInNAs rather than incorporation of nitrogen atoms. It was also confirmed experimentally that the N-radicals produced by RF-discharge are incorporated in the epitaxial layer like dopant atoms, indicating that their sticking coefficient is about one. This result is unlike that for the MOCVD growth using dimethylhydrazine as an N-source. These results are crucial to further improve the crystal quality of GaInNAs.

Metalorganic chemical vapor deposition of GaInNAs lattice matched to GaAs for long-wavelength laser diodes

The crystal growth of GaInNAs lattice matched to GaAs by metalorganic chemical vapor deposition using dimethylhydrazine as the nitrogen source is described for realizing long-wavelength laser diodes. It was found that the crystalline quality of GaInNAs on AlGaAs is improved by inserting a GaAs spacer layer between GaInNAs and AlGaAs. The photoluminescence spectra of GaAs/Ga 0.9In 0.1N y As 1− y /GaAs-DH was measured at room temperature with N content y of 1.5, 2.3 and 2.9%, respectively. The PL intensity decreases with increasing N content, though the lattice mismatch of GaInNAs layers to GaAs substrates decreases with increasing N content. We also produced the laser diodes with GaInNAs active layer and measured the N content dependence of the threshold current density. With increasing N content, the threshold current density increases with the reduction of PL intensity. We made it clear that GaInNAs material system is applicable to a 1.3 μm laser diode on a GaAs substrate. We expect to achieve a good lasing performance at 1.3 μm with the most suitable growth condition and design of laser diodes.