Post-growth Rapid Thermal Annealing Research Articles

Nature and Formation of Non-Radiative Defects in GaNAs And InGaAsN

AbstractThe optically detected magnetic resonance (ODMR) technique has been employed to examine the nature and formation mechanism of non-radiative defects in GaNAs and InGaAsN. In both alloys, two defects were observed and were shown to be deep-level, non-radiative recombination centers. One of the defects has been identified as a complex involving an AsGa antisite. These two defects gain more importance with increasing N composition up to 3%, presumably due to an increase in their concentration. With a further higher N composition, the defects start to lose importance in carrier recombination that is attributed to an increasingly important role of other new non-radiative channels introduced with a high N composition. On the other hand, effect of In composition up to 3% seems to be only marginal. Both defects were shown to be preferably introduced in the alloys during low-temperature growth by molecular beam epitaxy (MBE), but can be rather efficiently removed by post-growth rapid thermal annealing.

High nitrogen composition GaAsN by atmospheric pressure metalorganic vapor-phase epitaxy

Highly luminescent GaAs 1− x N x alloys were successfully grown by atmospheric pressure metalorganic vapor-phase epitaxy (MOVPE). The nitrogen composition x of as high as 5.6% was obtained using trimethylgallium (TMGa), tertiarybutylarsine (TBAs) and dimethylhydrazine (DMHy) precursors. In-situ and post-growth rapid thermal annealing was performed to enhance the optical quality of the material. Intense low temperature photoluminescence was obtained from GaAsN down to 0.9 eV (1.38 μm).

Investigation of defects in low-temperature-grown GaAs using optical transient spectroscopy

Optical transient current spectroscopy (OTCS) has been used to investigate defects in the low-temperature-grown GaAs after postgrowth rapid thermal annealing (RTA). Two samples A and B were grown at 220°C and 360°C on (0 0 1) GaAs substrates, respectively. After growth, samples were subjected to 30 s RTA in the range of 500–800°C. Before annealing, X-ray diffraction measurements show that the concentrations of the excess arsenic for samples A and B are 2.5×10 19 and 1×10 19 cm −3, respectively. It is found that there are strong negative decay signals in the optical transient current (OTC) for the annealed sample A. Due to the influence of OTC strong negative decay signals, it is impossible to identify deep levels clearly from OTCS. For a comparison, three deep levels can be identified for sample B before annealing. They are two shallower deep levels and the so-called As Ga antisite defect. At the annealing temperature of 600°C, there are still three deep levels. However, their structures are different from those in the as-grown sample. OTC strong negative decay signals are also observed for the annealed sample B. It is argued that OTC negative decay signals are related to arsenic clusters.

Effects of interdiffusion on the luminescence of InAs/GaAs quantum dots covered by InGaAs overgrowth layer

We have studied the effects of postgrowth rapid thermal annealing on the optical properties of 3-nm-height InAs/GaAs quantum dots covered by 3-nm-thick In x Ga 1− x As ( x =0, 0.1, and 0.2 ) overgrowth layer. At higher annealing temperature ( T⩾750°C), the photoluminescence peak of InGaAs layer has been observed at lower-energy side of the InAs quantum-dot peak. In addition, the blueshift in photoluminescence (PL) emission energy is found to be similar for all samples with increasing the annealing temperature from 650 to 850°C. However, the trend of narrowing of photoluminescence linewidth is significantly different for InAs quantum dots with different In mole fractions in InGaAs overgrowth layer. These results suggest that the intermixing in the lateral direction plays an important role in helping to understand the modification of optical properties induced by rapid thermal annealing.

Evolution from point defects to arsenic clusters in low-temperature grown GaAs/AlGaAs multiple quantum wells

Optical transient current spectroscopy (OTCS), photoluminescence (PL) spectroscopy and excitonic electroabsorption spectroscopy have been used to investigate the evolution of defects in the low-temperature grown GaAs/AlGaAs multiple quantum well structures during the postgrowth rapid thermal annealing. The sample was grown at 350°C by molecular beam epitaxy on miscut (3.4° off (0 0 1) towards (1 1 1) A) (0 0 1) GaAs substrate. After growth, the sample was subjected to 30 s rapid thermal annealing in the range of 500–800°C. It is found that the integrated PL intensity first decreases with the annealing temperature, then gets a minimum at 600°C and finally recovers at higher temperatures. OTCS measurement shows that besides As Ga antisites and arsenic clusters, there are several relatively shallower deep levels with excitation energies less than 0.3 eV in the as-grown and 500°C-annealed samples. Above 600°C, OTCS signals from As Ga antisites and shallower deep levels become weaker, indicating the decrease of these defects. It is argued that the excess arsenic atoms group together to form arsenic clusters during annealing.

Annealing effect on the surface morphology and photoluminescence of InGaAs/GaAs quantum dots grown by molecular beam epitaxy

Postgrowth rapid thermal annealing was performed on InGaAs/GaAs quantum dots grown by molecular beam epitaxy. The blue shift of the emission peak and the narrowing of the luminescence line width are observed at lower annealing temperature. However, when the annealing temperature is increased to 850°C, the emission line width becomes larger. The TEM image of this sample shows that the surface becomes rough, and some large clusters are formed, which is due to the interdiffusion of In, Ga atoms at the InGaAs/GaAs interface and to the strain relaxation. The material is found to degrade dramatically when the annealing temperature is further increased to 900°C, while emission from quantum dots can still be detected, along with the appearance of the emission from excited state.

Effects of rapid thermal annealing on self-assembled InGaAs/GaAs quantum dots superlattice

Postgrowth rapid thermal annealing was used to study the relaxation mechanism and optical properties of InGaAs/GaAs self-assembled quantum dots superlattice grown by molecular beam epitaxy. It is found that a significant narrowing of the luminescence linewidth (from 80 to 42 meV) occurs together with about 86 meV blue shift at annealing temperature up to 950°C. Double crystal X-ray diffraction measurements show that the intensity of the satellite diffraction peak, which corresponds to the quantum dots superlattice, decreased with the increasing annealing temperature and disappeared at 750°C, but recovered and increased again at higher annealing temperatures. This behavior can be explained by two competing relaxation mechanisms; interdiffusion and favored migration. The study indicates that a suitable annealing treatment can improve the structural properties of the quantum dots superlattice.

Be diffusion in InGaAs, InGaAsP epitaxial layers and across InGaAs/InGaAsP, InGaAs/InP heterointerfaces

The diffusion of Be during post-growth Rapid Thermal Annealing (RTA) in InGaAs, InGaAsP, InGaAs/InGaAsP and InGaAs/InP epitaxial structures grown by Gas Source Molecular Beam Epitaxy (GSMBE) has been studied. The observed Secondary Ion Mass Spectrometry (SIMS) concentration distributions, obtained for annealing cycles with time durations of 10–240 s and temperatures in the range of 700–900°C for Be doping concentration of 3×10 19 cm −3, could be explained by kick-out mechanism considering the neutral Be interstitial species and positively charged group-III self-interstitials.

Growth and postgrowth rapid thermal annealing of InAsN/InGaAs single quantum well on InP grown by gas source molecular beam epitaxy

InAsN/InGaAs single quantum wells (SQWs) with different nitrogen concentration have been successfully grown on InP substrates by gas source molecular beam epitaxy used rf plasma nitrogen source. Photoluminescence (PL) results of the as-grown samples show red-shifted PL peak energy and rapidly degraded intensity as the nitrogen concentration increases. The roughly estimated maximum nitrogen mole fraction in these samples is 0.4%. Both the PL intensity and linewith of these InAsN/InGaAs SQWs were significantly improved after postgrowth rapid thermal annealing with the optimum temperature at 525–550 °C for samples with different nitrogen content. The improvement on 10 K PL intensity can be as high as 230 times, and the room temperature PL intensities of the annealed InAsN SQWs have been comparable to those of InAs SQWs used for laser diodes. Quantum well intermixing (QWI) induced blue-shifted PL spectra were also observed in these samples. The QWI threshold temperature decreases as the nitrogen concentration increases, which indicates that defects created by nitrogen incorporation may enhance the QWI.

Redistribution of Be in InGaAsP layers grown by GSMBE during post-growth annealing

In this work we present results of beryllium diffusion during the post-growth rapid thermal annealing at 700–900°C in InGaAsP layers grown by GSMBE. The experimental structure consist of a 2000 A Be-doped layer (3×1019 cm–3) In0.73Ga0.27As0.58P0.42 layer sandwiched between 5000 A undoped In0.73Ga0.27As0.58P0.42 layers. A kick-out model of the substitutional-interstitial diffusion mechanism, which involves neutral Be interstitial species and positively charged group III self-interstitials, is proposed to explain the observed SIMS depth profiles.

Time-Resolved Photoluminescence Studies of InxGa1−xAs1−yNy

AbstractTime-resolved photoluminescence spectroscopy has been used to investigate carrier decay dynamics in InxGa1−xAs1−yNy (x ∼ 0.03, y ∼ 0.01) epilayers grown on GaAs by metalorganic chemical vapor deposition. Time-resolved PL measurements, performed for various excitation intensities and sample temperatures, indicate that the broad PL emission at low temperature is dominated by localized exciton recombination. Lifetimes in the range of 0.07–0.34 ns are measured; these photoluminescence lifetimes are significantly shorter than corresponding values obtained for GaAs. In particular, we observe an emission energy dependence of the decay lifetime at 10 K, whereby the lifetime decreases with increasing emission energy across the PL spectrum. This behavior is characteristic of a distribution of localized states, which arises from alloy fluctuations. We have also studied the effects of post-growth rapid thermal annealing (RTA) on the integrated photoluminescence emission intensity, which indicate that the optimal annealing conditions is 690 °C when annealed for 120 seconds in a nitrogen ambient.

Modelling and simulation of beryllium diffusion in InGaAs compounds grown by gas source molecular beam epitaxy

The diffusion of Be during post-growth rapid thermal annealing (RTA) in InGaAs layers grown by gas source molecular beam epitaxy (GSMBE) has been studied. The observed secondary ion mass spectrometry (SIMS) concentration distributions, obtained for annealing cycles with time durations of 10 s to 240 s and temperatures in the range for Be doping concentration of , could be explained by a kick-out mechanism considering neutral Be interstitials and singly positively charged group III self-interstitials. Be and Ga, In interstitial diffusivities, the equilibrium concentration of Ga and In interstitials, as a function of temperature, are obtained from this work.

Room temperature operation of epitaxially grown Si/Si0.5Ge0.5/Si resonant interband tunneling diodes

Resonant interband tunneling diodes on silicon substrates are demonstrated using a Si/Si0.5Ge0.5/Si heterostructure grown by low temperature molecular beam epitaxy which utilized both a central intrinsic spacer and δ-doped injectors. A low substrate temperature of 370 °C was used during growth to ensure a high level of dopant incorporation. A B δ-doping spike lowered the barrier for holes to populate the quantum well at the valence band discontinuity, and an Sb δ-doping reduces the doping requirement of the n-type bulk Si by producing a deep n+ well. Samples studied from the as-grown wafers showed no evidence of negative differential resistance (NDR). The effect of postgrowth rapid thermal annealing temperature was studied on tunnel diode properties. Samples which underwent heat treatment at 700 and 800 °C for 1 min, in contrast, exhibited NDR behavior. The peak-to-valley current ratio (PVCR) and peak current density of the tunnel diodes were found to depend strongly on δ-doping placement and on the annealing conditions. PVCRs ranging up to 1.54 were measured at a peak current density of 3.2 kA/cm2.

Effects of rapid thermal annealing on structure and luminescence of self-assembled InAs/GaAs quantum dots

Postgrowth rapid thermal annealing was used to modify the structural and optical properties of the self-assembled InAs quantum dots grown on GaAs substrates by molecular beam epitaxy. It is found that significant narrowing of the luminescence linewidth (from 78.9 to 20.5 meV) from the InAs dot layer occurs together with about 260 meV blueshift at annealing temperatures up to 850 °C. Observation of high-resolution transmission electron microscopy shows the existence of the dots under lower annealing temperatures but disappearance of the dots annealed at 850 °C. The excited-state-filling experiments for the samples show that the luminescence of the samples annealed at 850 °C exhibits quantum well-like behavior. Comparing with the reference quantum well, we demonstrate significant enhancement of the interdiffusion in the dot layer.

Study of beryllium diffusion mechanisms in InGaAs epitaxial layers grown by CBE

The aim of this work is to investigate beryllium diffusion during post-growth annealing in InGaAs epitaxial layers. Indeed, this undesirable diffusion may occur during thermal treatments of InGaAs/InP heterojunction bipolar transistors (HBTs), which can generate a limitation of frequency performances of these devices. Epitaxial structures have been grown by chemical beam epitaxy (CBE). After post-growth rapid thermal annealing (RTA) was performed, secondary ion mass spectrometry (SIMS) was used to characterize the Be depth profiles. In parallel with our experimental study, we consider two models of Be diffusion in InGaAs in the case of point defect nonequilibrium. First, a kick-out diffusion model with neutral Be interstitial species and charged point defects was studied. Then, a combined substitutional-interstitial diffusion model based on simultaneous diffusion by dissociative and kick-out mechanisms is suggested. Good agreements between experimental depth profiles and simulated curves have been obtained.

Post growth rapid thermal annealing of GaN: The relationship between annealing temperature, GaN crystal quality, and contact-GaN interfacial structure

Microstructure of GaN films grown by metalorganic chemical-vapor-deposition (MOCVD) on c-sapphire substrates has been accessed as a function of post-growth rapid thermal annealing (RTA) temperatures from 600 °C to 800 °C. The influence of the thermally modified, near-surface crystalline quality on sputtered WSi contact to GaN was also evaluated. Similar planar defects were observed in all heat treated samples; only their density differed. Our analyses demonstrated a strong relationship between the improved GaN crystal quality and postgrowth high-temperature thermal processing. The density of the near-surface defects was lowered by 61% as the annealing temperature was raised from 600 °C to 800 °C. Depression of the near-surface defects encouraged development of the β-W2N interfacial phase and promoted metal-semiconductor interface smoothness.

Low-threshold 840-nm laterally oxidized vertical-cavity lasers using AlInGaAs-AlGaAs strained active layers

We explore the use of a novel strained AlInGaAs-AlGaAs material system to achieve low-threshold current in oxide-apertured vertical-cavity lasers (VCLs) emitting near 850 nm. We report a low continuous-wave (CW) room-temperature threshold current of 290 /spl mu/A from top-emitting, 840-nm VCLs with a 5-/spl mu/m-wide thin-oxide aperture. The low-threshold current has been attributed to the use of strained active layers, which increase the gain and reduce the transparency current. We also studied the effects of post-growth rapid thermal annealing (RTA) on the characteristics of AlInGaAs-AlGaAs VCLs and found that RTA improves the material quality and significantly enhances VCL performance.

Beryllium diffusion in InGaAs compounds grown by chemical beam epitaxy

Be diffusion mechanisms during post-growth annealing have been investigated in p-type InGaAs epitaxial layers. These Be-doped InGaAs layers were grown between two undoped InGaAs layers. Annealing cycles with time durations of 30 s to 3 min and temperatures in the range of 500 - 800 for doping concentrations of , and were performed. It was found that there is no significant Be diffusion during post-growth rapid thermal annealing (RTA) for all doping levels if annealing is performed at 500 and 600 for a time under 1 min. The same observation was made for a Be concentration of with annealing at 700 for 30 s. For a doping level of , significant Be diffusion occurs for temperatures and durations greater than 700 and 1 min respectively. The shapes of the obtained curves represent a `double profile' giving rise to a concave region called a `kink'. It was deduced from the experiments that the Be effective diffusion coefficient is approximately constant for the high region of the concentration profiles and proportional to the square root of concentration for the low part of the experimental curves. Assuming the latter coefficient dependence, an effective diffusivity was substituted into Fick's second law and the resulting differential equation was solved numerically using an explicit finite-difference method. Good agreement was obtained between our depth profiles and the corresponding simulated distributions.

A Generalized Model of Beryllium Diffusion in InGaASs Epitaxial Structures Under Point Defect Nonequilibrium Conditions

ABSTRACTBeryllium diffusion during post-growth annealing is investigated in InGaAs epitaxial layers. Indeed, this undesirable diffusion may occur during thermal treatments of InGaAs/lnP Heterojunction Bipolar Transistors (HBT's), which can generate a limitation of frequency performances of these devices. Epitaxial structures have then been grown, one set by Chemical Beam Epitaxy (CBE), and another one by Gas Source Molecular Beam Epitaxy (GSMBE). The post-growth Rapid Thermal Annealing (RTA) was then performed, and Secondary Ion Mass Spectrometry (SIMS) has been used to characterize the Be depht profiles.In parallel with our experimental study, we propose two models of Be diffusion in InGaAs in the case of point defect nonequilibrium. First, a Kick-out Diffusion model considering neutral Be interstitial species and charged point defects has been studied. Then, a Generalized Substitutional-Interstitial Diffusion model based on simultaneous diffusion by Dissociative and Kick-out mechanisms is proposed. Good agreements between experimental depth profiles and simulated curves have been obtained.

Epitaxial CeO2 on Silicon Substrates and the Potential of Si/CeO2/Si for SOI Structures

ABSTRACTCeO2 is nearly lattice matched to Si and has the CaF2 cubic structure thus it offers the potential for the epitaxial growth of an insulating film on Si. Laser ablation of a CeO2 target in an ultra high vacuum system was used for the deposition of single crystal CeO2. The effect of post growth thermal and rapid thermal annealing in O2, N2 and Ar atmosphere was found to have pronounced effects on the electrical properties measured by C-V and the optical properties measured by photoluminescence.We report on our initial results for the growth of epitaxial Si on the deposited CeO2 using low pressure CVD. Both RHEED and TEM studies showed that single crystal epitaxial Si was deposited on CeO2. The details of the Si deposition on CeO2 films for potential of SOI (silicon on insulator) structures will be discussed.