Heteroepitaxial InP Research Articles

The stability of elastically strained nanorings and the formation of quantum dot molecules

Self-assembled nanorings have recently been identified in a number of heteroepitaxially strained material systems. Under some circumstances these rings have been observed to break up into ring-shaped quantum dot molecules. A general non-linear model for the elastic strain energy of non-axisymmetric epitaxially strained nanostructures beyond the small slope assumption is developed. This model is then used to investigate the stability of strained nanorings evolving via surface diffusion subject to perturbations around their circumference. An expression for the fastest growing mode is determined and related to experimental observations. The model predicts a region of stability for rings below a critical radius, and also a region for larger rings which have a proportionally small thickness. The predictions of the model are shown to be consistent with the available results. For the heteroepitaxial InP on In 0.5 Ga 0.5 P system investigated by Jevasuwan et al. (2013) , the nanorings are found to be stable below a certain critical size. This is in good quantitative agreement with the model predictions. At larger sizes, the rings are unstable. The number of dots in the resulting quantum dot molecule is similar to the mode number for the fastest growing mode. Second order terms show that the number of dots is expected to reduce as the height of the ring increases in proportion to its thickness. The strained In 0.4 Ga 0.6 As on GaAs nanorings of Hanke et al. (2007) are always stable and this is in accordance with the findings of the analysis. The Au nanorings of Ruffino et al. (2011) are stable as well, even as they expand during annealing. This observation is also shown to be consistent with the proposed model, which is expected to be useful in the design and tailoring of heteroepitaxial systems for the self-organisation of quantum dot molecules. • Epitaxially strained, semiconductor nanorings have been observed to break-up into discrete mounds forming a so-called quantum dot molecule. • The non-linear, second order elastic strain energy of a generalised in-plane surface traction expressed in polar coordinates acting on an isotropic half-space is derived. • This is used to determine the stability of nanorings subject to circumferential perturbations. • Stability maps show that nanorings below a certain radius or thickness are always stable. • The growth mode of unstable perturbations is shown to closely correlate with the observed number of mounds in observed quantum dot molecules.

Defect reduction in heteroepitaxial InP on Si by epitaxial lateral overgrowth

Epitaxial lateral overgrowth of InP has been grown by hydride vapor phase epitaxy on Si substrates with a thin seed layer of InP masked with SiO2. Openings in the form of multiple parallel lines as ...

Nucleation Layer의 표면 거칠기가 GaAs 기판 위에 성장된 InP 에피층의 품질에 미치는 영향

Department of Electronic Engineering, Cheongju University, Cheongju 360-764, Korea(Received July 4, 2012; Revised July 11, 2012; Accepted July 12, 2012)Abstract: Heteroepitaxial InP films have been grown on GaAs substrates to study the effects of the nucleation layer's surface roughness on the epitaxial layer's quality. For this, InP nucleation layers were grown at 400℃ with various ethyldimethylindium (EDMIn) flow rates and durations of growth, annealed at 620℃ for 10 minutes and then InP epitaxial layers were grown at 550℃. It has been found that the nucleation layer's surface roughness is a critical factor on the epitaxial layer's quality. When a nucleation layer is grown with an EDMIn flow rate of 2.3 μmole/min for 12 minutes, the surface roughness of the nucleation layer is minimum and the successively grown epitaxial layer's qualities are comparable to those of the homoepitaxial InP layers reported. The minimum full width at half maximum of InP (200) x-ray diffraction peak and that of near-band-edge peak from a 4.4 K photoluminescence are 60 arcmin and 6.33 meV, respectively.Keywords: InP, Heteroepitaxy, Surface roughness, Nucleation layer

Selective area heteroepitaxy through nanoimprint lithography for large area InP on Si

AbstractThe use of nanoimprint lithography, a low cost and time saving alternative to E‐beam lithography, for growing heteroepitaxial indium phosphide layer on silicon is demonstrated. Two types of patterns on 500 nm and 200 nm thick silicon dioxide mask either on InP substrate or InP seed layer on silicon were generated by UV nanoimprint lithography: (i) circular openings of diameter 150 nm and 200 nm and (ii) line openings of width ranging from 200 nm to 500 nm. Selective area growth and epitaxial lateral overgrowth of InP were conducted on these patterns in a low pressure hydride vapour phase epitaxy reactor. The epitaxial layers obtained were characterized by atomic force microscopy, scanning electron microscopy and micro photoluminescence. The growth from the circular openings on InP substrate and InP (seed) on Si substrate is extremely selective with similar growth morphology. The final shape has an octahedral flat top pyramid type geometry. These can be used as templates for growing InP nanostructures on silicon. The grown InP layers from the line openings on InP substrates are ∼ 2.5 μm thick with root mean square surface roughness as low as 2 nm. Completely coalesced layer of InP over an area of 1.5 mm x 1.5 mm was obtained.The room temperature photoluminescence intensity from InP layers on InP substrate is 55% of that of homoepitaxial InP layer. The decrease in PL intensity with respect to that of the homoepitaxial layer is probably due to defects associated with stacking faults caused by surface roughness of the mask surface. Thus in this study, we have demonstrated that growth of heteroepitaxial InP both homogeneously and selectively on the large area of silicon can be achieved. This opens up the feasibility of growing InP on large area silicon for several photonic applications (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Improved structure and performance of the GaAsSb/InP interface in a resonant tunneling diode

GaAsSb/InP(1 0 0) hetero-interfaces were studied with regard to the performance of metal organic chemical vapor deposition (MOCVD)-grown p-type resonant tunneling diodes (RTDs). For that, thin InP layers were grown by MOCVD on the ternary compound GaAs 0.5 Sb 0.5 , which is lattice-matched to InP(1 0 0). Two different surface reconstructions of (1 0 0) GaAs 0.5 Sb 0.5 , similar to a reconstruction of either (1 0 0) GaAs or (1 0 0) GaSb, were used for preparing the InP/GaAs 0.5 Sb 0.5 hetero-interfaces: the As-rich, c (4×4) and the Sb-rich, (1×3) reconstructions. The preparation of the RTDs was identical except for the Sb- versus As-rich reconstruction of GaAsSb. The RTDs with As-rich prepared GaAsSb/InP interfaces showed significantly more symmetric I – V characteristics than those with the Sb-rich interface preparation, demonstrating a clear advantage for the As-rich interface preparation. Surfaces were measured in-situ with reflectance difference spectroscopy (RDS) and analyzed in ultrahigh vacuum (UHV) with low-energy electron diffraction (LEED) with regard to the sharpness of the interface. The RD spectra of thin hetero-epitaxial InP layers grown on GaAsSb (1 0 0) were compared to the well-established RD spectrum of MOCVD-prepared homo-epitaxial, (2×1)-like reconstructed P-rich InP (1 0 0), that was used as reference for a well-defined surface. Growing InP on the c (4×4) reconstructed GaAsSb (1 0 0) surface resulted in a significantly sharper interface than InP growth on (1×3) reconstructed GaAsSb(1 0 0), a result that was also borne out by high-resolution X-ray diffraction spectra.

In situ monitoring and benchmarking in UHV of InP/GaAsSb heterointerface reconstructions prepared via MOVPE

Abstract Thin InP layers were grown by metalorganic vapor phase epitaxy on the ternary compound GaAs0.5Sb0.5 lattice matched to InP(1 0 0). The heterojunctions were studied with in situ reflectance anisotropy spectroscopy and benchmarked in ultrahigh vacuum with ultraviolet and X-ray photoelectron spectroscopy and low energy electron diffraction with regard to the sharpness of the interface. During growth of GaAs0.5Sb0.5 an Sb-rich ( 1 × 3 ) -like reconstruction was observed and during stabilization with TBAs an As-rich c ( 4 × 4 ) reconstruction. These two different reconstructions of GaAs0.5Sb0.5(1 0 0), well-known from the binaries GaSb(1 0 0) and GaAs(1 0 0) respectively, were used for preparing InP/GaAs0.5Sb0.5 heterojunctions. The RA spectra of thin heteroepitaxial InP layers were compared to a well-established RA spectrum of MOVPE-prepared homoepitaxial, ( 2 × 1 ) -like reconstructed P-rich InP(1 0 0), that was used as a reference spectrum of a well defined surface. Growing InP on the c ( 4 × 4 ) reconstructed GaAsSb(1 0 0) surface resulted in a significantly sharper interface than InP growth on ( 1 × 3 ) reconstructed GaAsSb(1 0 0).

GaAs 기판 위에 EDMIn과 TBP로부터 성장되고 양극산화 처리된 InP Schottky Diode

Au/oxide/n-InP Schottky diodes were fabricated from heteroepitaxial InP layers grown on GaAs substrates by the metalorganic vapor phase epitaxy (MOVPE) method from a new combination of source materials: ethyldimethylindium (EDMIn) and tertiarybutylphosphine (TBP). Anodic oxidation technique by using a solution of 10 g of ammonium pentaborate in 100 cc of ethylene glycole as the electrolyte was used to deposit a thin oxide layer. The barrier heights determined from three different techniques, current-voltage (I-V) measurements at room temperature and in the temperature range of 273 K - 373 K, and room temperature capacitance-voltage (C-V) measurements are in good agreement, 0.7 - 0.9 eV which is considerably high as compared to the 0.45 - 0.55 eV in Au/n-InP Schottky diode without a Passivation layer. The ideality factors of 1.1 - 1.3 of the Schottky diodes were also determined from the I-Y characteristics. Deep level transient spectroscopy (DLTS) studies revealed only one shallow electron state at 92.6 meV below the bottom of the conduction band and no deep state in the heteroepitaxial InP layers grown from EDMIn and TBP.

Elastic and anelastic properties of Fe-doped InP films on silicon cantilevers

The effect of Fe doping on the elastic and anelastic properties of heteroepitaxial InP films on microfabricated silicon cantilevers has been investigated by the vibrating-reed technique (typical frequencies 100 Hz to 10 kHz) with strain amplitudes in the range of 10−6 to 10−3 and in the temperature interval from 113 to 508 K. A matter of particular interest has been the effect of iron doping on the motion and multiplication of dislocations which are known to restrict the application of the material for instance in optoelectronic devices. For this purpose, the amplitude dependence of damping as well as internal friction as a function of temperature, thermal treatment, and frequency have been investigated and are discussed in terms of the present knowledge about twins and dislocations in InP. In addition, Young’s modulus as well as film stress have been measured as a function of temperature, which permits an estimate of the thermal expansion coefficient.

Thermal decomposition of InP surfaces: volatile component loss, morphological changes, and pattern formation

The thermal decomposition of bulk and heteroepitaxial InP surfaces is studied by in-situ scanning electron microscopy combined with mass spectrometry and atomic force microscopy. Correlation is established between the evaporation of phosphorous and the formation of thermal etch pits. The formation of the pattern that the In droplets constitute is analysed using fractal mathematics. Only negligible roughening is induced by annealing outside the pits.

“Compliant” twist-bonded GaAs substrates: The potential role of pinholes

By twist wafer bonding, thin (100) GaAs layers were transferred onto (100) GaAs handling wafers in order to fabricate structures like those suggested in the literature as “compliant universal substrates.” Heteroepitaxial InP and InGaAs films were grown on the GaAs twist-bonded layers. Twisted and untwisted grains of the epitaxial film with diameters from 0.1 to several μm without threading dislocations were observed by transmission electron microscopy. Twisted grains grew on the twist-bonded layer, while the untwisted grains grew directly on the GaAs handling wafer and were caused by pinholes in the twist-bonded GaAs layer. It is suggested that the lateral limitation of the epitaxial growth of grains on the thin twisted GaAs layer caused by the presence of pinholes reduces the density of threading dislocations in the strain-relaxed film and might be a mechanism for the observed low density of threading dislocations in lattice-mismatched epitaxial films grown on twist-bonded “compliant universal substrates.”

Thermal decomposition of bulk and heteroepitaxial (100) InP surfaces: A combined in situ scanning electron microscopy and mass spectrometric study

The thermal decomposition of bulk and heteroepitaxial (100) InP surfaces is studied by in situ scanning electron microscopy combined with mass spectrometry. The onset of P evaporation coincides with the In droplet nucleation at about 480 °C and the major evaporation of phosphorous commences above 510 °C and corresponds to the serious deterioration of the surface. There is no significant difference between bulk and defected (heteroepitaxial InP/GaAs) samples. The relevance to InP technology is discussed.

A comparative study of heterostructures InP/GaAs (001) and InP/GaAs (111) grown by metalorganic chemical vapor deposition

Heteroepitaxial InP layers were grown under the same growth conditions by metalorganic chemical vapor deposition on (001), (111)A, and (111)B surfaces of GaAs substrates. The heteroepilayers were studied by transmission electron microscopy, high-resolution x-ray diffraction, low-temperature photoluminescence, and low-temperature photoluminescence excitation. It is demonstrated that good quality InP epitaxial layers can be grown on GaAs substrates. Since layers and substrates have the same crystal structure, but different lattice parameters (aGaAs=5.6535 Å, aInP=5.8687 Å), the accommodation at the interface may occur by the formation of misfit dislocations parallel to the heterointerface. A remarkable reduction of the threading dislocation density for the (111) orientation and a decrease in the full width at half maximum values of the x-ray diffraction peaks were obtained. These results signify a dramatic crystalline improvement due to the reduction of the dislocation density using (111)-oriented GaAs substrates. The efficient photoluminescence and the full width at half maximum of the exciton peak compared with that of InP homoepitaxy show that good quality InP epilayers can be obtained on (111)-oriented GaAs substrates. The strain relaxation was investigated by high-resolution x-ray diffraction, and low-temperature photoluminescence excitation. The difference between the optical and the x-ray diffraction results is attributed to the thermoelastic strain due to the difference in the thermal expansion coefficients between epilayers and substrates.

Electrical deactivation of interstitial Zn in heteroepitaxial InP by hydrogen and its effect on electronic properties

Hydrogen passivation of InP layers grown on lattice-mismatched substrates can achieve thermally stable deactivation of dislocation-related deep levels, making this a promising process for improving the performance of heteroepitaxial InP space solar cells. However, in addition to dislocation-related defects, interstitial Zn (Zni) defects that are characteristic of Zn-doped InP and which form deep donor states within the InP band gap, are important considerations for optimizing the electronic quality of these layers. Here, we show that hydrogen forms complexes with and deactivates Zni donor states within Zn-doped InP grown by metalorganic chemical vapor deposition. A combination of photoluminescence (PL), electrochemical capacitance–voltage dopant profiling, secondary ion mass spectroscopy and current–voltage (I–V) measurements are applied to a set of samples receiving systematic hydrogenation and annealing treatments. We find that the deactivation of Zni deep donors, as detected by monitoring the evolution of the donor–acceptor transition using PL measurements, causes an increase of ∼50% in the net acceptor concentration of heavily Zn-doped heteroepitaxial InP by elimination of the acceptor compensation effect due to active Zni donors. Analysis of I–V characteristics indicates that Zni passivation sharply reduces depletion region recombination and shunt currents within heteroepitaxial diodes, causing an increase in the diode turn-on voltage from 680 to 960 mV. Subsequent annealing above 500 °C reactivates the Zni defects, resulting in a systematic increase in doping compensation as well as a decrease in VTO toward the original, as-grown value. A study of the reactivation kinetics for the H–Zni complex reveals a greater thermal stability than that of H–Zn acceptor complexes but less than that of H-dislocation complexes in InP, with an estimated dissociation energy for the H–Zni complex of 2.3 eV. While these effects are observed for both homoepitaxial and heteroepitaxial Zn-doped layers, the effect is far more pronounced for the heteroepitaxial layers due to the relatively high Zni concentration in the latter.

Hydrogen passivation of interstitial Zn defects in hetero-epitaxial InP cell structures and influence on device characteristics

Hydrogen passivation of hetero-epitaxial InP solar cells is of interest for deactivation of dislocations and other defects caused by the cell/substrate lattice mismatch that currently limits the photovoltaic performance of these devices. Here we show that in addition to passivation of dislocations, hydrogen deactivates interstitial Zn donor defects present within the Zn-doped emitter of metal organic chemical vapor deposition (MOCVD)-grown p+n hetero-epitaxial InP devices. Zn interstitial passivation increases the forward bias turn-on voltage of hetero-epitaxial InP diodes by as much as 280 mV over the non-hydrogenated value, reaching a value of 960 mV which is close to that obtained for homo-epitaxial diodes. The increase is reproducible and is not observed for either n+p structures or homo-epitaxial p+n structures. Through a combination of photoluminescence, C–V profiling, SIMS and I–V measurements we explain that the source of the voltage enhancement is a combination of decreased acceptor compensation in the emitter and decreased current losses due to depletion region recombination and shunting paths associated with the high concentration of Zn interstitials in Zn-doped hetero-epitaxial InP. © 1997 John Wiley & Sons, Ltd.

Hydrogen passivation of interstitial Zn defects in hetero‐epitaxial InP cell structures and influence on device characteristics

Hydrogen passivation of heteroepitaxial InP solar cells is of recent interest for deactivation of dislocations and other defects caused by the cell/substrate lattice mismatch that currently limit the photovoltaic performance of these devices. In this paper we present strong evidence that, in addition to direct hydrogen-dislocation interactions, hydrogen forms complexes with the high concentration of interstitial Zn defects present within the p(+) Zn-doped emitter of MOCVD-grown heteroepitaxial InP devices, resulting in a dramatic increase of the forward bias turn-on voltage by as much as 280 mV, from ~680 mV to ~960 mV. This shift is reproducible and thermally reversible and no such effect is observed for either n(+)p structures or homoepitaxial p(+)n structures grown under identical conditions. A combination of photoluminescence (PL), electrochemical C-V dopant profiling, SIMS and I-V measurements were performed on a set of samples having undergone a matrix of hydrogenation and post-hydrogenation annealing conditions to investigate the source of this voltage enhancement and confirm the expected role of interstitial Zn and hydrogen. A precise correlation between all measurements is demonstrated which indicates that Zn interstitials within the p(+) emitter and their interaction with hydrogen are indeed responsible for this device behavior.

High beginning-of-life efficiency p/n InP solar cells

The high electrical conversion performance and radiation resistance of InP solar cells was discovered during the last decade. The combination of these two characteristics makes InP a very attractive material for space solar cells. To date, the best performance results for both homo-epitaxial and hetero-epitaxial InP solar cells were achieved using an n/p configuration. The p/n configuration is desirable for hetero-epitaxial growth on inexpensive, strong, lightweight group IV substrates such as Si and Ge. Furthermore, diffused-junction p/n cells demonstrated a higher radiation resistance than the n/p configuration cells; however, the testing of the p/n configuration was limited to lower quality cells as judged by their beginning-of-life (BOL) efficiencies. We have succeeded in developing p/n configuration homo-epitaxy InP solar cells with BOL efficiency values exceeding 17.6p tested under air mass zero (AM0) conditions. The high efficiency values obtained from our cells resulted from improved emitter performance, which was due to better control of the growth of Zn-doped p-type InP. © 1997 John Wiley & Sons, Ltd.

Structural and optical characterization of InP grown on Si(111) by metalorganic vapor phase epitaxy using thermal cycle growth

Heteroepitaxial InP layers were grown on Si(111) by metalorganic vapor phase epitaxy using thermal cycle growth. The best crystallographic and optical quality was obtained when thermal cycle growth was begun after only a thin InP layer had been deposited. High resolution x-ray diffraction rocking curves of 4.8 μm thick InP layers yield full widths at half-maximum as low as 76 arc s and show that epilayers have a positive tilt with respect to the substrate. Cross-section transmission electron microscopy observations and Rutherford backscattering measurements show that thermal cycling induces a net reduction of defect density in the interfacial region. Photoluminescence (PL) measurements performed on the best quality thermal cycle grown sample show a thermal strain induced energy splitting of 3.8 meV between the free exciton emissions associated with heavy and light holes. Two other peaks in the PL spectra correspond to acceptor-bound (A0,X)mj=±3/2 and (A0,X)mj=±1/2 excitonic transitions, as confirmed by photoluminescence excitation measurements. Their full width at half-maxima are 1.4 and 0.9 meV, respectively, for the optimized samples. They may be associated with Si acting as an acceptor.

Photoreflectance Study on the Effect of Lattice Defects in InP on (001) Si

The residual stress in epitaxial InP on (001) Si was investigated by photoreflectance spectroscopy. Depending on doping concentration, low-field and intermediate-field spectra were measured which were quantitatively analysed by a third-derivative approximation or by a multilayer model, respectively. In both cases, transitions only from the heavy-hole and the split-off valence subbands into the conduction band contributed to the spectra, while the light-hole to conduction-band transition was absent. In addition to the energy shift due to tensile strain caused by the different thermal expansion coefficients of InP and Si, a signal component originating from compressive strain in the InP was observed. This effect is attributed to the clustering of dislocations at twin defects. As a result, a model of the defect distribution in the heteroepitaxial InP layers was presented.

The effect of dislocations on the optical absorption of heteroepitaxial InP and GaAs on Si

The optical absorption of heteroepitaxial InP and GaAs layers grown on exactly [001]-oriented Si substrates was investigated by spectroscopic ellipsometry combined with anodic stripping. In the wavelength range above the band-gap-equivalent wavelength considerable absorption was found which depends on the dislocation density in the layer. A theoretical model based on the electric microfield of charged dislocations was developed which agrees closely with the experimental results. After calibration differential spectroscopic ellipsometry was used to determine the dislocation-density profile in the InP and GaAs layers. Thus, the dislocation density could be determined in the region of a few tens of nm to the heterointerface of InP on Si where the identification and counting of dislocations is impossible by other methods.

Hydrogen passivation of n+p and p+n heteroepitaxial InP solar cell structures

High-efficiency, heteroepitaxial (HE) InP solar cells, grown on GaAs, Si or Ge substrates, are desirable for their mechanically strong, light-weight and radiation-hard properties. However, dislocations, caused by lattice mismatch, currently limit the performance of the HE cells. This occurs through shunting paths across the active photovoltaic junction and by the formation of deep levels. In previous work we have demonstrated that plasma hydrogenation is an effective and stable means to passivate the electrical activity of dislocations in specially designed HE InP test structures. In this work, we present the first report of successful hydrogen passivation in actual InP cell structures grown on GaAs substrates by metalorganic chemical vapor deposition (MOCVD). We have found that a 2 hour exposure to a 13.56 MHz hydrogen plasma at 275 C reduces the deep level concentration in HE n+n InP cell structures from as-grown values of approximately 10(exp 15)/cm(exp -3), down to 1-2 x 10(exp 13)/cm(exp -3). The deep levels in the p-type base region of the cell structure match those of our earlier p-type test structures, which were attributed to dislocations or related point defect complexes. All dopants were successfully reactivated by a 400 C, 5 minute anneal with no detectable activation of deep levels. I-V analysis indicated a subsequent approximately 10 fold decrease in reverse leakage current at -1 volt reverse bias, and no change in the forward biased series resistance of the cell structure which indicates complete reactivation of the n+ emitter. Furthermore, electrochemical C-V profiling indicates greatly enhanced passivation depth, and hence hydrogen diffusion, for heteroepitaxial structures when compared with identically processed homoepitaxial n+p InP structures. An analysis of hydrogen diffusion in dislocated InP will be discussed, along with comparisons of passivation effectiveness for n+p versus p+n heteroepitaxial cell configurations. Preliminary hydrogen-passivated HE InP cell results will also be presented.