InGaAsN Layers Research Articles

Doping of dilute nitride compounds grown by liquid phase epitaxy

The doping of dilute nitrides is an important point of the growth and processing technology for different optoelectronic devices based on these compounds. In this paper, both intentional and nonintentional doping of InGaAsN and GaAsSbN have been investigated by temperature-dependent Hall effect measurements. Dilute nitrides layers have been grown by low-temperature (Tcryst < 600 °C) liquid-phase epitaxy (LPE). The chemical elements Sn and Mg have been chosen as n-type and p-type dopants, respectively. All nominally undoped InGaAsN layers are n-type with free carrier concentration about one order of magnitude higher than layers not containing nitrogen and grown by LPE. This makes it difficult to obtain epitaxial layers with p-type conductivity with these compounds. However, high-quality n-type, p-type and nearly compensated GaAsSbN layers have been successfully grown covering a large range of carrier concentrations from 1015 to 6×1018 cm−3. The quality of the GaAsSbN layers has been evidenced by a good photoresponse with a low energy threshold extended down to 1.2 eV as obtained by surface photovoltage spectroscopy.

Dilute nitride InGaAsN and GaAsSbN layers grown by liquid-phase epitaxy for photovoltaic applications

Dilute nitride InGaAsN and GaAsSbN layers are grown by low-temperature liquid-phase epitaxy (LPE) on GaAs substrates and characterized in view of application in solar cells. The composition of the layers is determined by energy-dispersive X-ray spectroscopy. X-ray photoelectron spectroscopy measurements confirm the Sb content and provide information about the chemical bonding of the N atoms. The band gap values at room temperature assessed from surface photo-voltage and photoluminescence measurements are in good agreement. The experimental results show that the layers exhibit reproducible properties, including a good optical quality and a photosensitivity red limit extended in comparison to GaAs down to about 1.33 – 1.37 eV for InGaAsN and 1.19 – 1.23 eV for GaAsSbN layers. The results obtained highlight the capacity of the LPE for growing dilute nitride layers with good optical quality for photovoltaic applications.

Defect properties of InGaAsN layers grown as sub-monolayer digital alloys by molecular beam epitaxy

The defect properties of InGaAsN dilute nitrides grown as sub-monolayer digital alloys (SDAs) by molecular beam epitaxy for photovoltaic application were studied by space charge capacitance spectroscopy. Alloys of i-InGaAsN (Eg = 1.03 eV) were lattice-matched grown on GaAs wafers as a superlattice of InAs/GaAsN with one monolayer of InAs (&amp;lt;0.5 nm) between wide GaAsN (7–12 nm) layers as active layers in single-junction solar cells. Low p-type background doping was demonstrated at room temperature in samples with InGaAsN layers 900 nm and 1200 nm thick (less 1 × 1015 cm−3). According to admittance spectroscopy and deep-level transient spectroscopy measurements, the SDA approach leads to defect-free growth up to a thickness of 900 nm. An increase in thickness to 1200 nm leads to the formation of non-radiative recombination centers with an activation energy of 0.5 eV (NT = 8.4 × 1014 cm−3) and a shallow defect level at 0.20 eV. The last one leads to the appearance of additional doping, but its concentration is low (NT = 5 × 1014 cm−3) so it does not affect the photoelectric properties. However, further increase in thickness to 1600 nm, leads to significant growth of its concentration to (3–5) × 1015 cm−3, while the concentration of deep levels becomes 1.3 × 1015 cm−3. Therefore, additional free charge carriers appearing due to ionization of the shallow level change the band diagram from p-i-n to p-n junction at room temperature. It leads to a drop of the external quantum efficiency due to the effect of pulling electric field decrease in the p-n junction and an increased number of non-radiative recombination centers that negatively impact lifetimes in InGaAsN.

Annealing effect on effective mass of two-dimensional electrons in InGaAsN/GaAsSb type II quantum well

The InP-based InGaAs/GaAsSb type II multiple quantum well is the system for developing optical devices for 2 – 3 μm wavelength regions. By doping nitrogen into InGaAs layers, the system becomes effective to fabricate the optical devices with longer wavelength. The epitaxial layers of InGaAsN/GaAsSb on InP substrates are grown by the molecular beam epitaxy. The electrical resistance has been measured as a function of the magnetic field up to 9 Tesla at several temperatures between 2 and 8 K. The effective mass is obtained from the temperature dependence of the amplitude of the Shubnikov-de Haas oscillations. We have reported the nitrogen concentration dependence of the effective mass on the InGaAsN/GaAsSb type II system. The effective mass increases as the nitrogen concentration increases from 0.0 to 1.5 %. In this report, the annealing effect on the effective mass is investigated. The effective mass decreases by the annealing. This result suggests that some amount of nitrogen atoms of the InGaAsN layers are considered to diffuse to the GaAsSb layers by the annealing.

Effect of Sb in thick InGaAsSbN layers grown by liquid phase epitaxy

Dilute nitride InGaAsSbN layers grown by low-temperature liquid phase epitaxy are studied in comparison with quaternary InGaAsN layers grown at the same growth conditions to understand the effect of Sb in the alloy. The lattice mismatch to the GaAs substrate is found to be slightly larger for the InGaAsSbN layers, which is explained by the large atomic radius of Sb. A reduction of the band gap energy with respect to InGaAsN is demonstrated by means of photoluminescence (PL), surface photovoltage (SPV) spectroscopy and tight-binding calculations. The band-gap energies determined from PL and ellipsometry measurements are in good agreement, while the SPV spectroscopy and the tight-binding calculations provide lower values. Possible reasons for these discrepancies are discussed. The PL spectra reveal localized electronic states in the band gap near the conduction band edge, which is confirmed by SPV spectroscopy. The analysis of the power dependence of the integrated PL has allowed determining the dominant radiative recombination mechanisms in the layers. The values of the refraction index in a wide spectral region are found to be higher for the Sb containing layers.

Experimental study of the effect of local atomic ordering on the energy band gap of melt grown InGaAsN alloys

We present a study of melt grown dilute nitride InGaAsN layers by x-ray photoelectron spectroscopy (XPS), Raman and photoluminescence (PL) spectroscopy. The purpose of the study is to determine the degree of atomic ordering in the quaternary alloy during the epitaxial growth at near thermodynamic equilibrium conditions and its influence on band gap formation. Despite the low In concentration (∼3%) the XPS data show a strong preference toward In–N bonding configuration in the InGaAsN samples. Raman spectra reveal that most of the N atoms are bonded to In instead of Ga atoms and the formation of N-centred In3Ga1 clusters. PL measurements reveal smaller optical band gap bowing as compared to the theoretical predictions for random alloy and localised tail states near the conduction band minimum.

Nitrogen incorporation into GaAsN and InGaAsN layers grown by liquid‐phase epitaxy

AbstractThis paper presents the comparison of nitrogen incorporation in GaAsN and InGaAsN layers grown on GaAs substrate from Ga‐ and In‐rich solution, respectively, by liquid‐phase epitaxy. Polycrystalline GaN has been used as a source of nitrogen in two cases. The initial epitaxy temperature has been varied in the temperature range 600‐550 °C. Nitrogen content in Ga1‐xAsNx grown layers has been determined to be in the range 0.1‐0.5%. Higher nitrogen incorporation efficiency has been found for quaternary InGaAsN layers grown under carefully chosen lattice matched conditions. The incorporation of nitrogen into GaAsN and InGaAsN layers has been study by vibrational mode absorption spectroscopy. Nitrogen‐induced vibration mode near 472 cm‐1 has been registered in GaAsN samples. Preferential In‐N bonds and the formation of N‐centred In3Ga1 clusters have been identified for lattice matched to GaAs epitaxial InGaAsN layers. Electrical properties of the samples have been characterized by temperature‐dependent Hall effect measurements. Nominally undoped GaAsN and InGaAsN grown layers are n‐type with Hall concentration about one order of magnitude higher in comparison to layers not containing nitrogen. Thermally activated increase in the free carrier concentration at temperatures higher than 150 K is observed which indicates the presence of N‐related deep donor levels below dilute nitride conduction band edge. (© 2013 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Structural and electrical characteristics of InGaAsN layers grown by LPE

Crystallographic and transport properties of nominally undoped and Sn-doped InGaAsN layers grown by low-temperature LPE have been studied and related to the growth conditions.In the case of lattice matching, flat and uniform mirror-like layers of 8–10μm in thickness are obtained. The compositions of the layers under study have been determined by combination of X-ray microanalysis and X-ray diffraction methods to be In0.035Ga0.065As0.086N0.014. The lattice mismatch between layer and substrate Δal/as calculated from X-ray diffraction curves is less than−7×10−4 for all samples. The layers grown at lower epitaxy temperatures exhibit the highest crystalline quality, better lattice match and better homogeneity. This is in good agreement with the results of morphological study by atomic force microscopy which show root mean-square surface roughness of 0.18nm for the best layers.CV and Hall measurements reveal that intentionally undoped InGaAsN layers are n-type with free carrier concentration about one order of magnitude higher in comparison to layers not containing nitrogen and high electron mobility values over 2000cm2/Vs. A dramatic reduction in the free carrier concentration and slightly increase in mobility are observed for Sn-doped InGaAsN layers.

N incorporation and photoluminescence in In-rich InGaAsN grown on InAs by liquid phase epitaxy

Dilute nitride InGaAsN layers with high In content have been grown on InAs substrates by liquid phase epitaxy using GaN as a precursor for N in the growth solution. Photoluminescence (PL) was obtained in the mid-infrared spectral range at temperatures between 4 and 300 K. Although Ga increases the InAs bandgap, the strong band anti-crossing effect from the N incorporation resulted in an overall bandgap reduction of 11 meV compared with InAs. The temperature-dependent PL exhibited a complicated behaviour and showed an anomalous increase in intensity from 190 K to room temperature. This was due to the formation in a complex defect which behaves as a non-radiative recombination centre and prevents radiative band–band recombination at temperatures <190 K. Above this temperature the PL increases as band–band transitions become allowed. The formation of this defect requires the presence of both Ga and N and becomes de-activated after a high-temperature anneal. Raman spectroscopy confirmed the presence of phonon modes associated with In–N and Ga–N bonds confirming the incorporation of N using liquid phase growth.

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 &amp; Co. KGaA, Weinheim)

Low-temperature LPE growth and characterization of InGaAsN thick layers

Abstract This work demonstrates the possibility for low-temperature Liquid-Phase Epitaxy (LPE) growth of lattice matched to GaAs substrate dilute nitride InGaAsN layers with good crystalline quality and high Hall electron mobility. X-ray microanalysis and X-ray diffraction methods have been used to determine the composition and crystalline quality of the grown InGaAsN layers. Surface roughness is examined by atomic force microscopy. N-related local vibration modes are observed by Raman scattering. The Hall electron mobility and free carrier concentration have been measured in the temperature range 80-300K by conventional Van der Pauw method.

Study of melt-grown GaAsN and InGaAsN epitaxial layers

This paper presents investigation of electronic transport properties of GaAsN and InGaAsN epitaxial layers with low nitrogen content, the so called dilute nitrides, grown by liquid-phase epitaxy (LPE). The layers up to 2 microns thick have been grown from Ga- and In-rich melt at different initial epitaxy temperatures in the range 660–620 °C. Polycrystalline GaN has been used as a source for nitrogen. As grown, unintentionally doped GaAsN and InGaNAs are n-type with free carrier concentrations one order of magnitude higher than those for the reference nitrogen free undoped GaAs and InGaAs layers. Lattice matched to GaAs substrate InGaAsN layers exhibit Hall mobility values higher than 2000 V/cm2.s

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.

Methods of controlling the emission wavelength in InAs/GaAsN/InGaAsN heterostructures on GaAs substrates

Studies of the properties of InGaAsN compounds and methods of controlling the emission wavelength in InAs/GaAsN/InGaAsN heterostructures grown by molecular beam epitaxy on GaAs substrates are reviewed. The results for different types of heterostructures with quantum-size InGaAsN layers are presented. Among those are (1) traditional InGaAsN quantum wells in a GaAs matrix, (2) InAs quantum dots embedded in an (In)GaAsN layer, and (3) strain-compensated superlattices InAs/GaAsN/InGaAsN with quantum wells and quantum dots. The methods used in the study allow controllable variations in the emission wavelength over the telecommunication range from 1.3 to 1.76 μm at room temperature.

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 &gt; 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.

Structural investigation of InGaAsN films grown on pseudo-lattice-matched InGaAs substrates by metalorganic vapor phase epitaxy

The use of the nearly lattice-matched In x Ga 1 −x As pseudo-substrate has been explored for the growth of In x Ga 1 −x As 1 −y N y with higher In ( x) contents by metalorganic vapor phase epitaxy (MOVPE). As compared with the quality of high In-containing In 0.3Ga 0.7As 0.98N 0.02 films grown directly on GaAs substrates, the growth on In 0.2Ga 0.8As pseudo-lattice-matched substrates yielded good structural quality films. The number of misfit dislocations investigated by cross-sectional transmission electron microscopy was found to be reduced in the InGaAsN grown layer. Furthermore, higher optical quality In 0.3Ga 0.7As 0.98N 0.02 films with the bandgap of 1.01 eV were grown on the In 0.2Ga 0.8As pseudo-lattice-matched substrate. This study shows that the use of the In x Ga 1 −x As pseudo-lattice-matched substrate is an effective method to fabricate a thick lattice-matched InGaAsN layers with higher optical and structural qualities necessary for the development of the multijunction (MJ) solar cells.

Properties of InGaAsN heterostructures emitting at 1.3–1.55 µm

A comparative study of two types of heterostructures with quantum-size InGaAsN/GaAs layers in a GaAs matrix formed by molecular beam epitaxy is performed. The first type of heterostructure consists of InGaAsN layers deposited in a conventional continuous mode. The active part of the second type of heterostructure (HS) is formed by submonolayer InAs insertion confined by InGaAsN HS layers, surrounded by short period GaAsN/InGaAsN superlattices. The structures under investigation emit in a wavelength range 1.3–1.55 µm at room temperature. It is shown that lower averaged nitrogen and indium concentrations are needed to realize the emission at 1.5 µm in the case of the second type of HS.

The Optical Properties of Heterostructures with Quantum-Confined InGaAsN Layers on a GaAs Substrate and Emitting at 1.3–1.55 μm

Under study is the photoluminescence of two types of MBE-grown heterostructures with quantum-confined InGaAsN/GaAs layers: (1) conventional InGaAsN quantum wells (QWs) in GaAs, and (2) heterostructures with an active region consisting of a short-period GaAsN/InGaAsN superlattice that has an InGaAsN QW with a submonolayer InAs insertion at its center. At room temperature, the structures under study emit light in the range from ∼1.3 to ∼1.55 μm. In the second type of heterostructure, emission with a wavelength larger than 1.5 μm can be obtained at lower nitrogen and indium concentrations than in a conventional QW. This leads to a significant depression of the effects related to decomposition of an InGaAsN solid solution, thus improving the radiative efficiency of the InGaAsN QWs.