Strain-induced Lateral-layer Ordering Research Articles

Tailoring detection wavelength of InGaAs quantum wire infrared photodetector

The authors report on tailoring detection wavelengths of InGaAs quantum wire infrared photodetectors, using different numbers of short-period superlattice (SPS) pairs to vary the thickness of quantum wires (QWRs) along the growth direction, prepared by the strain-induced lateral-layer ordering process. The QWR characteristics are maintained for QWRs using either In0.52Al0.24Ga0.24As or In0.52Al0.48As barriers and for thin QWR layers made of six SPS pairs. Sharp photoresponses at 6.3 and 8.4 μm are observed for quantum wire infrared photodetectors with ten and six SPS pairs, respectively.

Strain dependence on barrier material and its effect on the temperature stability of photoluminescence wavelength in self-assembled GaInAs quantum wires

The strain-induced lateral-layer ordering process was used to fabricate GaInAs quantum wire (QWR) heterostructures on InP whose QWR layers are separated by different barrier materials. Using cross-sectional transmission electron microscopy the microstructure of the different QWR samples was studied. It was found that GaInAs QWR heterostructures with nominally lattice matched AlGaInAs barriers resulted in heavily strained QWR regions relative to the same structure with nominally lattice matched AlInAs or InP barriers. Furthermore, photoluminescence studies demonstrate that these heavily strained QWR samples with AlGaInAs barriers have a wavelength-shift rate of 0.2 to 1.0 Å/°C in the 293–360 K range. This is in comparison to GaInAs QWR samples with ternary or binary barriers and a GaInAs quantum well control sample that have wavelength-shift rates of ∼2.5 and ∼6.0 Å/°C, respectively. It is shown empirically that a minimum amount of strain in the GaInAs QWR/AlGaInAs barrier region is required to achieve wavelength-shift rates below 1 Å/°C.

Self-assembled GaInAs quantum wire heterostructure design for temperature stabilized emission wavelength

The strain-induced lateral-layer ordering process is used to fabricate GaInAs quantum wire (QWR) heterostructures on (1 0 0)-InP via molecular beam epitaxy. Using photoluminescence (PL) spectroscopy, the effect of the barrier material between QWR layers on the peak PL behavior with respect to temperature is investigated. In addition, two types of growth interrupt schemes were used to optimize the PL characteristics of the QWR heterostructure. Growth pauses during the deposition of the QWR layer were explored as well as growth pauses in between the QWR layer and barrier material. Consequently, peak PL wavelengths stabilized to less than 1 Å/°C above room temperature have been obtained for GaInAs QWR heterostructures using nominally lattice-matched AlGaInAs barriers and QWR-barrier growth interrupts to improve PL intensity. It is shown that strain is the main factor behind this PL behavior with respect to temperature.

Temperature invariant lasing and gain spectra in self-assembled GaInAs quantum wire Fabry–Perot lasers

GaInAs quantum wire (QWR) heterostructures have been grown by molecular beam epitaxy using the strain-induced lateral-layer ordering (SILO) process. Broad-area Fabry–Perot QWR lasers have been fabricated from this material. The lasing wavelength from the QWR laser shifts at a rate of 0.9 Å/°C between 77 and 300 K compared to 4.6 Å/°C for a quantum well laser control sample. Furthermore, the gain spectra of the QWR laser are derived from the amplified spontaneous emission spectra at 77 and 300 K using the Hakki–Paoli method. The gain peak is also stabilized against temperature changes indicating that temperature stable lasing behavior seen in SILO grown GaInAs QWR Fabry–Perot laser diodes is due to a temperature stable band gap.

Temperature dependent polarization switching and band-gap anomalies in strained GaxIn1−xAs quantum wire heterostructures

We report on the polarized photoluminescence (PPL) properties of strained GaxIn1−xAs quantum wire (QWR) heterostructures formed in situ by the strain-induced lateral-layer ordering process. It is found that the PPL spectra of these QWRs have unique properties that depend on temperature and orientation of the pump polarization with respect to the QWR direction. In particular, the dominant polarization switches when the sample is warmed from 77 to 300 K provided the pump polarization is parallel to the QWRs. This indicates that the light-hole (LH) and heavy-hole (HH) bands cross with increasing temperature, which implies that the multiaxial strain in this material is a function of temperature. Furthermore, this effect is only observed in GaxIn1−xAs QWR heterostructures that display anomalous band-gap stability with respect to temperature. It is believed that the strain induced temperature dependent LH–HH crossing as evidenced by the polarization switching switching effect is responsible for this anomaly.

Growth optimization of GaxIn1−xAsyP1−y/GaAs(0.98 μm) quantum wire heterostructures

The strain-induced lateral-layer ordering technique has proven itself to be a viable method for creating quantum wires (QWRs) via molecular beam epitaxy. In an effort to achieve emission at the technologically important 0.98 μm wavelength, GaxIn1−xAsyP1−y QWRs formed on on-axis GaAs substrates using (GaP)m/(InAs)n short-period superlattices (SPS) are investigated. The growth parameters, such as the growth temperature, the source switching pause scheme, and the group-V source flow sequence are optimized to create QWRs with emission near 0.98 μm. For structures utilizing abrupt switching between constituent layers, it was determined that the optimal temperature at which to grow the (GaP)2.2/(InAs)1 SPS on GaAs was 480 °C. By introducing pause times and additional group-V source coverage to the growth scheme, the quality of the QWR heterostructure is markedly improved. The existence of a lateral composition modulation in the growth plane is evidenced by the low-energy emission (redshift) with respect to the bulk GaxIn1−xAsyP1−y, and the highly polarized nature of the photoluminescence (PL) spectra. Furthermore, the effects of the barrier material between QWR layers (in the growth direction) on the temperature stability of PL peak wavelengths near 0.98 μm were studied. The temperature induced wavelength shift depends on the barrier material, barrier thickness, and the composition of the SPS used in the QWR region. A minimum PL peak wavelength shift of about 200 Å between 77 and 300 K was observed in the GaxIn1−xAsyP1−y QWR system with Ga0.51In0.49P barriers.

Temperature stabilized 1.55 μm photoluminescence in strained GaxIn1−xAs quantum wire heterostructures

We present two techniques for manipulating the peak photoluminescence wavelength towards ∼1.55 μm, from the usual 1.61 μm, of strained GaxIn1−xAs quantum wire (QWR) heterostructures. The QWR samples have been prepared by the strain-induced lateral-layer ordering process during molecular beam epitaxy utilizing short-period superlattices of (GaAs)m/(InAs)n. The subscripts m and n refer to the number of deposited monolayers of GaAs and InAs, respectively. In the first approach, for some cases of m>n, the QWRs will contain more Ga thereby decreasing the 300 K wavelength towards 1.55 μm provided the strain is not too great. The second approach relies on post-growth annealing to shift the 300 K peak emission. For anneals performed at 650 °C for 3–5 h, 300 K wavelengths from 1.55 to 1.59 μm have been attained. Moreover, all of these samples display a unique behavior of peak PL with respect to temperature. Some samples show no net shift in wavelength over a range of 77–380 K. Other samples have 77 K wavelengths longer than their 300 K wavelengths. It is believed that these structures have the potential to be processed into temperature stabilized Fabry–Pérot lasers emitting at 1.55 μm.

The directionality of quantum confinement on strain-induced quantum-wire lasers

Optical properties of Ga0.47−xIn0.53+xAs (x∼0.14) multiple-quantum-wire (MQWR) lasers prepared by the strain-induced lateral-layer ordering process were studied. A typical ratio of threshold current density, ∼10, was observed from the GaInAs MQWR lasers with contact stripes aligned to the [110] ([110] MQWR laser) and the [1̄10] ([1̄10] MQWR laser) directions. The threshold current density of the [110] MQWR laser is ∼30% lower than that of a Ga0.47In0.53As multiple-quantum-well (MQW) reference laser. The 77 K lasing wavelengths were 1.46, 1.57, and 1.69 μm for the MQW laser, the [1̄10] and [110] MQWR lasers, respectively. This strong anisotropy of threshold current densities and lasing wavelengths is the first direct evidence of the directionality of two-dimensional quantum confinement in the MQWR structure.

Growth of GaInAsP quantum wire heterostructures using the strain-induced lateral-layer ordering process

Abstract We present a generalized strain-balance theory on the strain-induced lateral-layer ordering (SILO) process, where various combinations of short-period superlattice (SPS) constituents are used to fabricate novel quantum wire (QWR) heterostructures. Based on the theory, we have fabricated two sets of QWRs in the GaInP and GaInAsP material systems with emission wavelengths of 6200 A and 1 μm, respectively. Growth of ( GaP ) 2 ( InP ) 1 SPS was used to create QWRs on GaAs0.66P0.34-based substrates. Also, QWRs were formed using ( GaP ) 2.2 ( InAs ) 1 SPS on GaAs substrates. In both these cases, the monolayer pairings of the SPS constituents were unequal. Transmission electron microscopy and polarized photoluminescence spectroscopy confirm the formation of QWRs. These results support the validity of the generalized theory of the SILO process.

Temperature-insensitive photoluminescence above 300 K in strained GaxIn1 − x As multiple quantum wire heterostructures

Stable peak wavelength photoluminescence (PL) spectra has been observed in Ga x In 1 − x As strained multiple quantum wire (MQWR) heterostructures over a temperature range between 250 and 380 K. The MQWR samples were grown in situ by molecular beam epitaxy using the strain-induced lateral-layer ordering (SILO) process to create the quantum wires. The formation of the strained Ga x In 1 − x As quantum wires and the amount of the strain associated with the wires depends on the growth conditions and structural configuration of the MQWR active region. Samples grown near a substrate temperature of 500°C show a negligible net PL peak wavelength shift between 77 and 380 K. Red shifts and blue shifts of PL peak wavelengths between 77 and 380 K are observed in samples grown at temperatures less than and greater than 500°C, respectively. Due to the multi-axial strain fields induced by the SILO process in the MQWR active regions, the PL peak wavelength of all the MQWR samples stabilize at ∼ 1.61 μ m for temperatures above 250 K. The temperature dependent shift of peak PL wavelength between room temperature and 72°C for these MQWR heterostructures is as low as 0.2 Å/°C.

Visible wavelength (6470 Å) GaxIn1−xP/GaAs0.66P0.34 quantum wire heterostructures

Utilizing the strain-induced lateral-layer ordering (SILO) process, we have grown GaxIn1−xP multiple quantum wires (MQWR) on ternary GaAs0.66P0.34 substrates using a modified strain-balance mechanism. The resulting [110] lateral modulation occurred with a periodicity of ∼300 Å. Two dimensions of quantum confinement were obtained by surrounding the laterally confined GaxIn1−xP regions by layers of higher-energy-gap Al0.15Ga0.53In0.32P in the growth direction. A redshift in the photoluminescence emission was observed as the growth temperature was increased attributed to a stronger lateral composition modulation at the higher growth temperatures. Based on the modified strain-balance mechanism, light-emitting diodes with the GaxIn1−xP MQWR active region were fabricated using the SILO process. Strongly TE-polarized room-temperature electroluminescence from these devices was observed at 6470 Å.

Interdiffusion of lateral composition modulated (GaP)2/(InP)2 short-period superlattices with different encapsulants

The interdiffusion of lateral composition modulated (GaP)2/(InP) 2 short-period superlattices (SPSs) is reported. The lateral composition modulation is achieved by the strain induced lateral layer ordering (SILO) process. A blueshift in the interband transition is observed by photoluminescence spectroscopy for capless and SiO 2 encapsulated annealed SPSs (800 °C, 5.5 h), while the intensity and wavelength of Si3N4 encapsulated annealed SPSs are only slightly perturbed. From transmission electron microscopy, capless annealed SPSs (800 °C, 5.5 h) retain their lateral composition modulation, however, the (001/2) satellite reflections disappear. For long anneal times (48 h), the interband transition corresponds to that of a In0.50Ga 0.50P alloy, suggesting the lateral composition modulation disappears. The observed lateral interdiffusion coefficient exceeds the vertical by a factor of ∼30, suggesting SPS interdiffusion is enhanced by native point defects.

Observation of temperature-insensitive emission wavelength in GaInAs strained multiple-quantum-wire heterostructures

We report on the photoluminescence (PL) properties of GaxIn1−xAs strained multiple-quantum-wire (MQWR) heterostructures formed in situ by the strain-induced lateral-layer ordering (SILO) process. Samples with moderately strained MQWR active regions demonstrate a negligible variance in emitted PL spectra with respect to temperature. The net temperature dependence of PL wavelength for these samples is less than 0.1 Å/°C between 77 and 300 K. For MQWR samples with stronger lateral composition modulation, the PL peak wavelength blue shifts with increasing temperature. The SILO process induced multiaxial strain in the (GaAs)2/(InAs)2.2 short-period-superlattice active region is responsible for this temperature insensitivity and blueshift of PL wavelength with temperature.

GaxIn1−xAs quantum wire heterostructures formed by strain-induced lateral-layer ordering

GaxIn1−xAs quantum wire (QWR) arrays were grown on (100) on-axis InP substrates by single-step molecular-beam epitaxy. The QWRs were formed in situ in (GaAs)2/(InAs)2.2 short-period-superlattice (SPS) layers by the strain-induced lateral-layer ordering (SILO) process. An analysis of the cross-sectional and plan-view transmission electron microscopy images, photoluminescence peak energies, and polarization anisotropy has confirmed the QWR nature of these heterostructures. The SILO process occurs over a wide growth temperature range near 500 °C. However, both high and low growth temperatures result in a weaker lateral composition modulation. The strength of the lateral composition modulation is proportional to the total thickness of the SPS quantum-well layers, regardless of the thickness of the individual quantum well. In other words, the magnitude of composition modulation accumulates when growth proceeds. A strain-driven bulk solid-state diffusion model has been proven to be part of the driving force of the SILO process, in addition to a dynamic surface diffusion during growth.

Effect of substrate misorientation on the growth of GaxIn1−x P lateral quantum wells

We report the effects of misoriented GaAs substrates and varied substrate temperatures on the formation of GaxIn1−xP lateral quantum wells (LQWs) by the strain-induced lateral-layer ordering (SILO) process. Nominally [001] GaAs on-axis substrates, [001] substrates cut 2° off toward the [110] direction, and [001] substrates cut 2° off toward the [1̄10] direction were used to simultaneously grow LQWs. The samples were characterized using plan-view and cross-sectional transmission electron microscopy and polarized photoluminescence spectroscopy. We found that regardless of the substrate misorientation or substrate growth temperature, the SILO process induced LQWs always formed along the [1̄10] direction; primarily determined by the direction of the group-V dimer bonds on the surface during growth.

Strained AlGaInP quantum wire lasers

We report on the fabrication of strained separate-confinement heterostructure AlGaInP visible laser diodes with multiple quantum wire active regions formed in situ during gas source molecular beam epitaxy. Lateral composition modulation with a period on the order of 100 Å perpendicular to the growth direction occurs spontaneously during the growth of the (GaP) 2/(InP) 2 short-period superlattice active region by the strain-induced lateral-layer ordering (SILO) process. Individual laser diodes fabricated from the same wafer but emitting parallel and normal to the wire axis exhibit highly anisotropic properties, including large difference in threshold current, emission wavelength, and opposite polarizations. These effects are explained in terms of the strained quantum wire potential. The additional degree of quantum confinement in quantum wire structure reduces the threshold current density by a factor of > 2.7 when compared with an otherwise identical quantum well laser.

Growth of GaxIn1−xAs quantum wire heterostructures by the strain-induced lateral-layer ordering process

GaxIn1−xAs quantum wire (QWR) arrays were grown in situ by molecular beam epitaxy. A lateral composition modulation was achieved in the GaxIn1−xAs material system via the strain-induced lateral layer ordering process occurring spontaneously when (GaAs)n/(InAs)n short-period superlattices are grown on (100)-oriented on-axis InP substrates. The resulting quasiperiodic modulation of the GaxIn1−xAs composition, with a periodicity of 300 Å, offers a lateral quantum confinement along the growth plane. The quantum confinement in the growth direction is provided by sandwiching the thin (∼100 Å) laterally ordered GaxIn1−xAs layer between layers of bulk Al0.24Ga0.24In0.52As. The formation of the QWR array is confirmed by cross-sectional transmission electron microscopy and polarized photoluminescence measurements.

Formation of Quantum Wires by Strain-Induced Lateral-Layer Ordering Process: Growth Mechanism and Device Applications

AbstractGaxIn1−xAs and GaxIn1−xP quantum wire (QWR) arrays were grown by a single-step molecular beam epitaxy. Lateral Ga(In composition modulation perpendicular to the growth direction occurs spontaneously during the growth of (GaAs)m/(InAs)n or (GaP)m/(InP)n shortperiod superlattices on InP or GaAs substrates, respectively, by the strain-induced lateral-layer ordering (SILO) process, producing lateral quantum wells. This straightforward method employs standard on-axis (001)-oriented substrates, and requires no pre-growth substrate patterning, nor does it involve post-growth processing for the formation of QWRs. Both GaxIn1−xAs infrared (1.7 μm) lasers and GaxIn1−xP visible (0.7 μm) lasers with QWR active regions have been successfully fabricated. These lasers showed many unique features that have never been observed in quantum well lasers.

AlGaInP multiple quantum wire heterostructure lasers prepared by the strain-induced lateral-layer ordering process

We have established an in situ technique, the strain-induced lateral-layer ordering (SILO) process, whereby lateral composition modulation perpendicular to the growth direction occurs spontaneously during growth by gas source molecular beam epitaxy, producing lateral quantum wells. We have combined this new growth technique with standard quantum well laser growth technology to produce GaInP/AlGaInP strained multiple quantum wire (MQWR) heterostructure lasers. Transmission electron microscopy confirms the presence of laterally ordered MQWR arrays with a linear density of 10/sup 6/ cm/sup -1/. Emission spectra from these MBWR heterostructures exhibit quantized energies and significant polarization anisotropies. Photoluminescence emission energies are analyzed using an approximate strained quantum wire calculation. Electroluminescence spectra are studied both above and below the lasing threshold. Threshold current densities as low as 250 A/cm/sup 2/ are obtained under pulsed conditions at 77 K. The energies, polarizations, and threshold current densities vary according to the orientation of the contact stripe with respect to the MBWR array. These effects are explained in terms of the quantum wire potential, the strain fields present in the MQWR active region, and their effects on the band structure and the optical gain.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

GaxIn1−xP multiple-quantum-wire heterostructures prepared by the strain induced lateral layer ordering process

We report the in situ growth of GaxIn1−xP multiple-quantum-wire (MQWR) structures by gas source molecular beam epitaxy. The MQWRs were formed through a strain induced lateral layer ordering (SILO) process occurring spontaneously when (GaP)n/(InP)n short-period superlattices were grown on (100)-oriented on-axis GaAs substrates. In one sample, cross-sectional transmission electron microscopy estimated average quantum-wire cross sections of 50 Å×100 Å with lengths of over 3000 Å leading to a linear density of 100 wires/μm. The existence of the MQWRs is also supported by polarized photoluminescence spectroscopy. Anisotropy ratios for two orthogonal polarizations were measured to be an order of magnitude larger than any previously reported. These data support the existence of MQWRs and demonstrate that the SILO growth process is a consistent and reproducible method of MQWR fabrication.