Heteroepitaxial InP Layers Research Articles

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 0.5Sb 0.5, which is lattice-matched to InP(1 0 0). Two different surface reconstructions of (1 0 0) GaAs 0.5Sb 0.5, similar to a reconstruction of either (1 0 0) GaAs or (1 0 0) GaSb, were used for preparing the InP/GaAs 0.5Sb 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.

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.

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.

Hydrogen passivation of np and pn heteroepitaxial InP solar cell structures

Dislocations and related point defect complexes caused by lattice mismatch currently limit the performance of heteroepitaxial InP cells by introducing shunting paths across the active junction and by the formation of deep traps within the base region. We have previously demonstrated that plasma hydrogenation is an effective and stable means to passivate the electrical activity of such defects within heteroepitaxial InP layers. In this work, we present our first results on the hydrogen passivation of ac tual heteroepitaxial n+p and p+n InP cell structures grown on GaAs substrates by metal organic chemical vapor deposition (MOCVD). We have found that a 2-h exposure to a 13.56-MHz hydrogen plasma at 275°C reduces the deep level co ncentration in the base regions of both n+p and p+n heteroepitaxial InP cell structures from as-grown values of 5–7 × 1014 cm−3, down to 3–5 × 1012 cm−3. All dopants were successfully reactivated by a 400°C, 5-min anneal with no detectable activation of deep levels. Current-voltage (I-V) analysis indicated a subsequent ∼100-fold decrease in reverse leakage current at 1 V reverse bias, and an impro ved built-in voltage for the p+n structures. In addition to being passivated, dislocations are also shown to participate in secondary interactions during hydrogenation. We find that the presence of dislocations enhances hydrogen diffusion into the cell structure and lowers the apparent dissociation energy of Zn-H complexes from 1.19 eV for homoepitaxial Zn-doped InP to 1.12 eV for heteroepitaxial Zn-doped InP. This is explained by additional hydrogen trapping at dislocations subsequent to the r eactivation of Zn dopants after hydrogenation.

InAlAs/InGaAs metal-semiconductor-metal photodiodes heteroepitaxially grown on Si substrates

To study performance and reproducibility of photodiodes (PDs) on Si in the long-wavelength region, InAlAs/InGaAs metal-semiconductor-metal PDs were fabricated on high-quality heteroepitaxial InP layers on Si substrates. A dark current of 0.5–2×10−8 A and a responsivity of 0.05–0.15 A/W were reproducibly obtained, at least at one of the ±5 V bias voltages. These dark currents and responsivity are similar to those of PDs with the same structure fabricated on InP substrates. The PDs on Si have pulse responses with full widths at half-maximum of 150–600 ps.

Heteroepitaxial InP layers grown by metalorganic chemical vapor deposition on novel GaAs on Si buffers obtained by molecular beam epitaxy

Heteroepitaxial InP layers were grown by metalorganic chemical vapor deposition on novel GaAs buffer layers on Si substrates. The GaAs buffers were prepared by molecular beam epitaxy and show a reduced threading dislocation density achieved by inserting one nanometer thick Si interlayers. The structural and optoelectronic properties of the heteroepitaxial InP layers, which were investigated by transmission electron microscopy, x-ray diffraction, and photoluminescence spectroscopy, show improvements attributed to the optimized GaAs buffer layers.

Structural and optoelectronic properties and their relationship with strain relaxation in heteroepitaxial InP layers grown on GaAs substrates

Heteroepitaxial layers of InP with thickness D ranging from 0.1 to 6.0 μm were grown by low-pressure metalorganic chemical vapor deposition on (001) surfaces of GaAs substrates. Their dislocation structure, induced strains, and nature of the radiative recombinations were investigated as a function of D with transmission electron microscopy, x-ray diffraction, and photoluminescence spectroscopy. For D<2 μm, the films are highly dislocated with a tangle of interfacial and threading dislocations above the heterointerface. The spatial extent of the interfacial dislocations and the density of threading dislocations increase with increasing D. For D≳2 μm the portion of the layers away from the heterointerface by more than 1.5 μm shows a decrease in the density of threading dislocations and a dramatic improvement in the crystalline quality with increasing D. Typical dislocation densities in the neighborhood of the top surface are in the mid 107 cm−2 range when D surpasses 4.0 μm. Concomitant with the improved crystalline quality, the following observations are made. Firstly, the full width at half maximum of the x-ray rocking curves diminishes from values larger than 500 arcsec for D<1.0 μm to about 200 arcsec for D≳4.0 μm. Secondly, the near-band-edge photoluminescence transitions, which for D<2.0 μm are predominantly determined by defect-induced band tailing, display excitonic character. Thirdly, below-band-gap transitions due to interfacial defects decrease in intensity. Biaxial compressive strain is present in the layers because of lattice mismatch and differences in linear thermal expansion with the substrate. The strain removes the degeneracy between the light- and heavy-hole states at the top of the valence band, and consequently with increasing temperature above 12 K recombinations from the conduction to the split valence bands are observed in the photoluminescence spectra for all D. The identification of such transitions follows from their temperature dependence and the activation energy yield for the thermalization of the holes. The measured valence-band splitting decreases from 12.5 meV for D=0.3 μm to saturation values of 5.6 meV for D≳3.0 μm, indicating strain relaxation with D in qualitative agreement with x-ray determinations. Quantitative differences between both methods are realized and are attributed to a temperature dependence of the differential linear thermal expansion. The contribution to the strain from the lattice mismatch is much larger than expected from equilibrium models. The dislocation generation at different stages during the growth is inferred from the strain relaxation against D and the observed location of the dislocations throughout the layers.