InGaAsN Layer Research Articles

Gamma-ray irradiation effect on planar defect evolution of lattice-matched InGaAsN/GaAs/Ge grown by MOVPE

This study explores structural changes in lattice-matched InGaAsN/GaAs/Ge films grown by MOVPE under gamma-ray irradiation. Exposure to a 60Co gamma rays at doses ranging from 0 to 2.0 MGy improved crystal uniformity by increasing surface grain size, reducing roughness from 8.328 nm to 3.512 nm. Planar defects in the GaAs layer traversed the InGaAsN layer, causing interface roughness. Electron diffraction patterns along the [110]-zone axis showed uniform alloy composition. TEM images revealed line contrasts at the GaAs/Ge interface extending into the InGaAsN layer, with boundary-like defects parallel to the growth direction. Additionally, (002) and (002‾) reflections, along with {111} planes, indicated planar defects, possibly antiphase boundaries. AFM and FESEM confirmed submicron-sized domains, characteristic of antiphase boundaries, in the InGaAsN film.

Annealing effects on the properties of InGaAsN/GaAsSb type‐II quantum well diodes grown on InP substrates

Annealing effects on the properties of InGaAsN/GaAsSb type‐II quantum well (QW) diodes grown on InP substrates by molecular beam epitaxy (MBE) were studied. It was found that the peak of electroluminescence (EL) shows drastic red‐shift and the reverse‐biased current of the current–voltage (I–V) characteristic of the type‐II QW diode increases by the annealing. In addition, we found that the electron effective mass of the InGaAsN layer of the type‐II InGaAsN/GaAsSb multiple quantum wells (MQWs) estimated by the temperature dependence of the amplitude of the Shubnikov‐de Haas (SdH) oscillations decreases by the annealing. The mechanism of the observed annealing effects was discussed.

GaAs/InGaAsN heterostructures for multi-junction solar cells

Solar-cell heterostructures based on GaAs/InGaAsN materials with an InAs/GaAsN superlattice, grown by molecular beam epitaxy, are studied. A p-GaAs/i-(InAs/GaAsN)/n-GaAs p–i–n test solar cell with a 0.9-μm-thick InGaAsN layer has an open-circuit voltage of 0.4 V (1 sun, AM1.5G) and a quantum efficiency of >0.75 at a wavelength of 940 nm (at zero reflection loss), which corresponds to a short-circuit current of 26.58 mA/cm2 (AM1.5G, 100 mW/cm2). The high open-circuit voltage demonstrates that InGaAsN can be used as a material with a band gap of 1 eV in four-cascade solar cells.

TEM Analysis of Planar Defects in InGaAsN and GaAs Grown on Ge (001) by MOVPE

InGaAsN on Ge (001) is proposed to be a part of the InGaP(N)/InGaAs/InGaAsN/Ge four-junction solar cell to increase a conversion efficiency over 40%. In this work, InGaAsN lattice-matched film and GaAs buffer layer grown on Ge (001) substrate by metal organic vapor phase epitaxy (MOVPE) were examined by transmission electron microscopy (TEM). Electron diffraction pattern of InGaAsN taken along the [110]-zone axis illustrates single diffracted spots, which represent a layer with a uniformity of alloy composition. Cross-sectional bright field TEM image showed line contrasts generated at the GaAs/Ge interface and propagated to the InGaAsN layer. Dark field TEM images of the same area showed the presence of boundary-like planar defects lying parallel to the growth direction in the InGaAsN film and GaAs buffer layer but not in the Ge substrate. TEM images with the (002) and (00-2) reflections and the four visible {111} planes reflections illustrated planar defects which are expected to attribute to antiphase boundaries (APBs). Moreover, the results observed from atomic force microscopy (AFM) and field emission electron microscopy (FE-SEM) demonstrated the surface morphology of InGaAsN film with submicron-sized domains, which is a characteristic of the APBs.

Fabrication of In 0.53 Ga 0.47 AsN 0.01 /AlAs 0.56 Sb 0.44 resonant tunnelling diodes grown on InP by molecular beam epitaxy

An In0.53Ga0.47AsN0.01/AlAs0.56Sb0.44 resonant tunnelling diode (RTD) has been fabricated by molecular beam epitaxy on InP substrates for the first time. A clear negative differential resistance (NDR) characteristic was observed at room temperature, where the peak/valley (P/V) ratio is as high as 19.6. This result indicates that the use of an InGaAsN layer in the RTD structure is very effective on obtaining an NDR characteristic with high P/V ratio.

Characterization of InGaAsSbN layers grown on InP by MBE

AbstractOptical and electrical properties of the InGaAsSbN layers grown by molecular beam epitaxy (MBE) on InP substrates were studied in comparison with InGaAsN layers. It was found that the optical properties of the InGaAsSbN layer characterized by photoreflectance (PR) and photoluminescence (PL) measurements are superior to those of InGaAsN layer. In addition, electrical properties characterized by Hall measurements were also improved by adding Sb atoms. Annealing studies on photoluminescence properties of the InGaAsSbN layer revealed that the PL intensity increases and the PL spectral half width decreases upon annealing up to 700 °C. These results indicate that post‐annealing is still necessary for InGaAsSbN layers to improve crystalline quality (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The dual role of nitrogen as alloying and confining element in GaAs-based dilute nitride semiconductors

We examine transport and relaxation dynamics of optically excited electrons in GaAs-based heterostructure layers, involving dilute nitrides in percent-level concentration range. Such heterostructures contain materials with very different mobilities. Drift instead of Hall mobility is determined using a special technique. The value of the mobility of photogenerated electrons in a freestanding, 3% N InGaAsN layer, as part of a two-layer structure of 100 nm GaAs/2 μm nitride, is found to be of the order of 2 cm2/Vs, much lower than other values reported in the literature. The concomitant presence of carriers in the GaAs and nitride layers leads to formation of a barrier at the interface region that hinders electrons to enter in the nitride material. The dwell time of photoexcited electrons in GaAs interfacing the nitride layer is of the order of milliseconds, as seen by photoconductivity transients after pulsed optical excitation, much longer than the resulted time from optical experiments. Comparison of optical with transport properties reveals that the same centers involved in luminescence, that appear to be extended, are responsible also for hopping transport, where they appear as deep states. A theoretical explanation is given.

Optical characterization of InGaAsN layers grown on InP substrates

Optical characterization of InGaAsN layers on InP substrates grown by molecular beam epitaxy (MBE) was carried out using photoluminescence (PL) and photoreflectance (PR) measurements. The PL wavelength coincides well with the energy gap ( E g) obtained by the PR measurement for the samples grown with various nitrogen compositions and growth temperatures. In particular, the sample which has the longest PL wavelength (2.03 μm at 300 K) shows a clear PR spectrum and the E g obtained by the PR measurement corresponds well with the PL peak energy, indicating that the emission at 2.03 μm is not a defect related emission but a band-edge emission of the InGaAsN layer.

Band offset of InGaAs(N)∕GaAs interfaces from first principles

Valence-band offsets of the InGaAs∕GaAs(001) and InGaAsN∕GaAs(001) interfaces are calculated from first principles. For InGaAs, we study the concentrations up to 25% of indium and for InGaAsN up to 12.5% of indium with 3% of nitrogen. Even though the band offset of the InGaAs∕GaAs interface has a nearly linear dependence on the indium concentration, band offset of the InGaAsN∕GaAs interface is strongly influenced by the amount of In–N bonds. Even a type-II band offset is found in the case of all indium located near to nitrogen and low strain of the InGaAsN layer.

A Comparison of the Structural Quality of High-In Content InGaAsN Films Grown on InGaAs Pseudosubstrate and on GaAs Substrate

The use of an InGaAs buffer layer was applied to the growth of thick InxGa1-xAs1-yNy layers with higher In contents (x > 30%). In order to obtain the lattice-matched InGaAsN layer having the bandgap of 1.0 eV, the In0.2Ga0.8As was chosen. In this work, the In0.3Ga0.7As0.98N0.02 layers were successfully grown on closely lattice-matched In0.2Ga0.8As buffer layers (InGaAsN/InGaAs). Structural quality of such layers is discussed in comparison with those of the In0.3Ga0.7As0.98N0.02 layers grown directly on the GaAs substrate (InGaAsN/GaAs). Based on the results of transmission electron microscopy, the misfit dislocations (MDs), which are located near the InGaAsN/GaAs heteroepitaxial interface, are visible by their strain contrast. On the other hand, no generation of the MDs is evidenced in the InGaAsN layer grown on the In0.2Ga0.8As pseudosubstrate. Our results demonstrate that a reduction of misfit strain though the use of the pseudosubstrate made possible the growth of high In-content InGaAsN layers with higher crystal quality to extend the wavelength of InGaAsN material.

InGaAsN Metal–Semiconductor–Metal Photodetectors with Transparent Indium Tin Oxide Schottky Contacts

GaAs-based photodetectors (PDs) draw much attention owing to several advantages, such as low fabrication cost and the mature process techniques. However, fabricating them is a difficult task for the lack of suitable absorption materials that can be coherently grown on the GaAs substrate. In this report, we provide another approach to fabricate GaAs-based PDs, in which the novel InGaAsN alloy is used as the absorption layer. Three structures of planar PDs were demonstrated using transparent indium tin oxide (ITO) contacts. The dark current of PDs were suppressed by applying the SiO2 Schottky-barrier enhancement layer, but the rough interface between the SiO2 and InGaAsN layer limited the device characteristics. Depositing a thin layer of ITO between the SiO2 and InGaAsN layers greatly improved the interface quality and the photo current-to-dark current ratio was also increased from 17.7 to 45.29 under 0.5 V bias.

Improvement of crystal quality of thick InGaAsN layers grown on InP substrates by adding antimony

We investigated the effect of adding Sb in 1-μm-thick InGaAsN layers grown by solid source molecular beam epitaxy (MBE) method on InP substrates. Secondary ion mass spectroscopy (SIMS) analysis of the InGaAsSbN layer showed that both the nitrogen and the Sb concentration are uniform in the growth direction. The X-ray rocking curve (XRC) of InGaAsSbN was narrower than that of the InGaAsN layer, which suggests that adding Sb improved the crystallographic quality of the thick InGaAsN layer. The surface morphology of the thick InGaAsSbN layer was as smooth as that of the lattice-matched InGaAs layer, while the surface of the thick InGaAsN layer was rough. These results indicate that the crystalline quality of thick InGaAsN layer can be improved by adding Sb. The photoluminescence (PL) peak wavelength became longer by adding Sb, but the PL intensity decreased. This is supposed to be due to the sensitivity of PL intensity to the growth condition.

Optical investigations on the surfactant effects of Sb on InGaAsN multiple quantum wells grown by MOVPE

In this report, the optical properties of the InGaAsN triple quantum wells were significantly improved by applying TMSb surfactant flow before the growth of InGaAsN layer. The PL intensities of the Sb-treated samples were improved by around two times and the line width of the emission spectrum was reduced from 263.6 to 67 meV as well, while maintaining the peak at 1265 nm. The surfactant effects of Sb were verified by photoluminescence, scanning probe microscopy (SPM) and high-resolution X-ray diffraction. The SPM measurement indicated that the surface condition was improved by Sb surfactant, and the surface roughness was reduced from 0.495 to 0.397 nm. In addition, the commonly observed localized effects of the InGaAsN QWs were also suppressed by Sb surfactant. Therefore, applying TMSb before the growth of InGaAsN could recover the degraded optical properties caused by nitrogen incorporation, and shows the potential to grow high-quality InGaAsN by MOVPE.

Evolution of Carrier Distribution and Defects in InGaAsN/GaAs Quantum Wells with Composition Fluctuation

Carrier distribution and defect induction in In0.34Ga0.66As0.98N0.02/GaAs single quantum wells grown by molecular beam epitaxy at low growth rates are investigated by frequency-dependent capacitance–voltage (C–V) and deep-level transient spectroscopy (DLTS). The C–V studies show that lowering the growth rate of the InGaAsN layer splits the carrier accumulation in the well into a central and two side peaks with different frequency dispersions. The DLTS studies show that a continuum of states (0–0.083 eV) and a deep trap at 0.21–0.25 eV are responsible for the central and the side peaks, respectively. A comparison with photoluminescence (PL) spectra shows that these defects are induced by composition fluctuation. Lowering the growth rate degrades composition fluctuation by segregating the material into an InGaAsN phase and an N-depleted phase. Post-growth annealing can remove the deep trap and improve the InGaAsN emission, confirming that the deep trap degrades the InGaAsN phase. The feature of the continuum of states suggests that it may be the structural defects associated with lattice expansion or localized states introduced by composition fluctuation.

Effect of growth rate on the composition fluctuation of InGaAsN∕GaAs single quantum wells

Effect of growth rate on the composition fluctuation is investigated in In0.34Ga0.66As0.98N0.02∕GaAs single quantum wells (QWs) by photoluminescence (PL), transmission electron microscopy, and admittance spectroscopy. In an InGaAsN layer grown at a normal growth rate, the PL spectra show a low-energy bump at the tail of an InGaAsN emission, suggesting the presence of composition fluctuation. Lowering the growth rate degrades the composition fluctuation by segregating into bimodal phases of an InGaAsN and InGaAs-rich phase. Further lowering the growth rate leads to a three-dimensional growth and enhances the InGaAs-rich phase. The carrier distribution for the InGaAsN layer grown at the normal rate shows a carrier bump at the tail of a strong accumulation peak, suggesting the presence of an electron state below the QW ground state. The admittance spectroscopy shows that the activation energy (32meV) of this electron state is comparable to the energy separation (30meV) between the InGaAsN emission and the low-energy bump, and thus it is possible that the composition fluctuation actually induces an electron state closely below the QW ground state.

A possibility of In–N fragments incorporation in InGaAsN MBE growth

We have investigated a possibility of the site-controlled InGaAsN epitaxy by using a new source material of hexakis-diethylamido-diindium ( [ In { N ( C 2 H 5 ) 2 } 3 ] 2 ) . In the site-controlled epitaxy of the InGaAsN layer, the N atoms should be incorporated randomly and should also preferentially form In–N bonds during growth. The new source has been developed to satisfy these two requirements for the site-controlled epitaxy. Single-crystalline InN layer has been successfully obtained on a nitrided α-Al 2O 3 substrate by supplying only a [ In { N ( C 2 H 5 ) 2 } 3 ] 2 beam. Polycrystalline InNAs has also been obtained on a nitrided α-Al 2O 3 substrate by [ In { N ( C 2 H 5 ) 2 } 3 ] 2 and an As 4 beam supplied simultaneously. Furthermore, phase separation into GaAs and InN phases has been observed in the layers grown under simultaneous irradiation of Ga, As 4 and [ In { N ( C 2 H 5 ) 2 } 3 ] 2 beams on a nitrided α-Al 2O 3 substrate. The results strongly indicate that site-controlled epitaxy can be expected to be achieved by using new source materials, such as [ In { N ( C 2 H 5 ) 2 } 3 ] 2 that can produce the In–N fragments efficiently.

Structural and optical properties of heterostructures with InAs quantum dots in an InGaAsN quantum well grown by molecular-beam epitaxy

Results obtained in a study of the structural and optical properties of GaAs-based heterostructures with InAs quantum dot layers overgrown with InGaAsN quantum wells are presented. Transmission electron microscopy has been applied to analyze how the thickness of the InGaAsN layer and the content and distribution of nitrogen in this layer affect the size of nanoinclusions and the nature and density of structural defects. It is shown that the size of InAs nanodomains and the magnitude of the lattice mismatch in structures containing nitrogen exceed those in nitrogen-free structures. A correlation between the luminescence wavelength and the size and composition of nanodomains is demonstrated. Furthermore, a correlation between the emission intensity and defect density in the structure is revealed.

Microstructures, defects, and localization luminescence in InGaAsN alloy films

We studied the structural and optical properties of InxGa1−xAs1−yNy (x = 0.116, ∼0.3 and y = 0–0.031) alloy films grown by low-pressure metalorganic vapour epitaxy (LP-MOVPE), performing high-resolution transmission electron microscopy (HRTEM) and photoluminescece (PL) measurements. The effects of rapid thermal annealing (RTA) at 700 °C under N2 ambient were also examined. The TEM images showed that with increasing In content, not only misfit dislocations near the InGaAsN/GaAs interface due to the large lattice mismatch with the GaAs subatrate, but also many defects in the InGaAsN layer due to the relaxation of local strain increased. From energy dispersive X-ray (EDX) analysis of the high In-content layers (x = 0.3–0.355), we found a significant In fluctuation in the InGaAsN layer. The PL peaks of In0.116Ga0.884As1−yNy (y = 0–0.031) measured at 7 K shifted to the high-energy side after RTA, while those of InxGa1−xAs1−yNy (x = ∼0.3, y = 0–0.015) shifted unusually to the low-energy side. This unsual behavior of the high In-content layer after RTA may be attributed to the enlargement of quantum-dot-like regions, which are formed by the compositional fluctuation in microscopic scale. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Influence of Be on N composition in Be-doped InGaAsN grown by RF plasma-assisted molecular beam epitaxy

Undoped and Be-doped InGaAsN layers were grown on GaAs substrates under the same growth conditions by radio frequency plasma-assisted molecular beam epitaxy. Increased tensile strain (Δ a/a=3×10 −3) was observed for Be-doped InGaAsN layers, compared to undoped InGaAsN layers. The strain is shown to originate from the increase in N composition related to Be incorporation, rather than solely from Be atoms substituting Ga atom sites (Be Ga). A possible reason is the high Be–N bond strength, which inhibits the loss of N from the growth surface during epitaxial growth, thereby increasing the N composition in the Be-doped InGaAsN layer.