Interface strain in organometallic vapor phase epitaxy grown InGaAs/InP superlattices

The spatial distribution of strain in organometallic vapor phase epitaxy grown InGaAs/InP superlattice structures has been studied by varying the thicknesses of the InGaAs well and the InP barrier layers and measuring the strain. High resolution x-ray diffraction rocking curves were used to measure the strain from angular separation between the zeroth-order superlattice peak and the substrate (004) peak. The results are consistent with a compressive strain resulting from arsenic carryover into the InP following InGaAs growth. The strain is not localized at the interfaces but extends into the InP barrier layer. The amount of arsenic carryover increases with the growth time of the InGaAs well.     

Selective growth of InP on patterned,nonplanar InP substrates by low-pressure organometallic vapor phase epitaxy

The effects of indium sources, mask materials and etched mesa profiles on growth mor-phology of Fe-doped semi-insulating InP on patterned, nonplanar InP substrates were studied for low-pressure organometallic vapor phase epitaxy (OMVPE). The presence or absence of polycrystalline InP layers deposited on the mask was found to depend on the indium source but not on the mask material. Trimethylindium was found to be the preferable indium source for prevention of polycrystalline InP deposits on the mask. The etched mesa shape was found to dominate the final geometry of the OMVPE re-grown InP layer. Inclusion of an interfacial layer of 1.16 μm bandgap wavelength InGaAsP between the dielectric mask and InP substrate produces a favorable mesa shape by con-trolling the level of undercut during mesa etching, so as to form a smooth mesa profile. After selective regrowth of InP over the resulting mesa, a planar surface is typically achieved for mesa stripes with a mask overhang length as long as 2.6 μm and a mesa height as high as 4 μm.     

High purity InP grown by chemical beam epitaxy

A Hall mobility as high as 176,200 cm²V⁻¹ s⁻¹ at 77 K withN _d -N _a =1.3×10¹⁴ cm⁻³ has been obtained by adjusting the substrate and the phosphine cracker temperatures. The 2 K photoluminescence spectra show finely resolved excitonic transitions for layers grown above 535° C with linewidths of 0.07 meV. Excitonic transitions have been recorded between 2 and 250 K. The free exciton energy position leads to a highly accurate expression of the band gap energy, which extrapolates toE _g =1.347 eV at 300 K.     

Step structure of GaInAsSb grown by organometallic vapor phase epitaxy

The surface step structure of Ga_1−xIn_xAs_ySb_1−y grown by organometallic vapor phase epitaxy on GaSb substrates has been studied by atomic force microscopy. Epilayers were grown at 525°C and 575°C on (001) GaSb substrates misoriented 2° toward (101) or 6° toward (1 1)B. For Ga_0.88In_0.12As_0.1Sb_0.9 grown at 575°C, the surface exhibits step-bunching on both types of substrates. When the composition is increased to Ga_0.86In_0.14As_0.12Sb_0.88, the periodic step structure breaks down and the surface becomes irregular. The deterioration of the step structure is a consequence of phase separation at the surface of the metastable GaInAsSb epilayer, which leads to the formation of GaAs- and InSb-rich regions. The photoluminescence (PL) of such layers show significant broadening due to carrier recombination in the lower energy gap InSb-rich quaternary regions. On the other hand, the surface of GaInAsSb epilayers grown at a lower temperature of 525°C is vicinal with steps heights of one to two monolayers. The PL FWHM values are considerably smaller for these layers. This improvement in material quality is related to smaller adatom lifetimes at the lower growth temperature. The importance of surface kinetics as it influences the step structure and thermodynamically driven phase separation is discussed.     

Atomic layer epitaxy of InP

In this work we will discuss the growth conditions for ALE of InP. Growth experiments were carried out in a LP-MOCVD system with a fast switch gas manifold. InP layers were deposited by pulsing TMIn and PH₃, using Argon as carrier gas. A self limiting growth rate at 1 ML/cycle has been obtained with a substrate temperature as low as 320-360° C. InP epitaxial layers were grown on GaAs and InP substrates, and on GaInAs(P) layers previously deposited by conventional MOCVD. Selective area epitaxy on InP using a Si₃N₄ mask was also demonstrated. Results of this study are very encouraging for hybrid MOCVD/ALE growth of In-based compounds.     

Oxygen incorporation,photoluminescence, and laser performance of AlGaAs grown by organometallic vapor phase epitaxy

Photoluminescence (PL) of separate confinement heterostructure, single quantum well (SCH-SQW) laser material provides a quantitative evaluation of the quality of AIGaAs grown by organometallic vapor phase epitaxy. There is a good correlation between the oxygen level in the quantum well confining layers measured by secondary ion mass spectroscopy, quantum well PL efficiency, and laser threshold current. When oxygen was reduced from 2.0 × 10¹⁸ cm⁻³ to 1.5 × 10¹⁷ cm^-3, the PL intensity increased by a factor of 12, and the threshold current density was improved from 1300 to 240 A/cm² for a 100 × 600 μm device. Oxygen levels were decreased by using a higher growth rate, shorter interface pause time, higher V/III ratio, and an arsine purifier.     

Interfaces of InAsP/InP multiple quantum wells grown by metalorganic vapor phase epitaxy

We present results of the growth of InAs_xP_1−x/InP strained heterostructures by low pressure metalorganic vapor phase epitaxy. A large incorporation of arsenic into the InAsP ternary was observed using tertiarylbutylarsine as precursor. High resolution x-ray diffraction, photoluminescence, and optical absorption measurements for InAsP/InP strained multiple quantum wells reveal that the InAsP/InP interface is very sensitive to growth interruption. A systematic study of a growth in terruption sequence designed to improve the InAs/InP interface was carried out. For nonoptimal growth interruption procedures a large density of interface states is created, probably as a consequence of compositional modifications within the interface region. We find that the absorption spectrum may reveal a significant density of interface states. Thus, photoluminescence on its own is insufficient to characterize the interface roughness even for structures showing narrow low-temperature photoluminescence peaks. We also observe an enhancement of the As content for structures grown on InP (001) relative to those simultaneously grown on InP(001) two degrees off toward [100], which suggests that the composition of As in the ternary is limited by its surface diffusion.     

Self-organization phenomenon of strained InGaAs on InP (311) substrates grown by metalorganic vapor phase epitaxy

We have demonstrated that a self-organization phenomenon occurs in strained InGaAs system on InP (311) substrates grown by metalorganic vapor phase epitaxy. This suggests that a similar formation process of nanocrystals exists not only on the GaAs (311)B substrate but also on the InP (311)B substrate. However, the ordering and the size homogeneity of the self-organized nanocrystals are slightly worse than those of the InGaAs/AlGaAs system on the GaAs (311)B substrate. The tensilely strained condition of a InGaAs/InP system with growth interruption in a PH₃ atmosphere reveals a surface morphology with nanocrystals even on the InP (100) substrate. It was found that strain energy and high growth temperature are important factors for self-organization on III-V compound semiconductors. Preliminary results indicate that the self-organized nanostructures in strained InGaAs/InP systems on InP substrates exhibit room temperature photoluminescent emissions at a wavelength of around 1.3 p.m.     

Photoluminescence characterization of solution and lec grown InP

Low temperature photoluminescence and electrical measurements on bulk grown polycrystalline and single crystal InP indicate the purity and crystal perfection to be equivalent to that of LPE and VPE samples. This work was supported in part by the U.S. Army Research Office, Research Triangle Park, N.C.; Defense Research Projects Agency, Arlington, VA; and Rome Air Development Center, Hanscom Air Force Base, Massachusetts.     

GaInAs/InP quantum wires grown by metalorganic vapor phase epitaxy on V-grooved InP substrates

A single nominally lattice matched GaInAs quantum well (QW)/quantum wire (QWR) structure was grown by metalorganic vapor phase epitaxy (MOVPE) in V-grooved InP substrates. Different Si0₂ etch masks with opening widths from 2 μm down to 200 nm (for application as second order DFB grating) were defined by optical and electron beam lithography. A damage-reduced wet chemical etching process enables the growth of the GaInAs QWs/QWRs without any InP buffer layer. In low temperature photoluminescence we found improved intensity for all wire structures prepared by this etching technique. A reduction of the period and opening width of the V-groove etch mask resulted in a optimized luminescence intensity ratio between QW and QWR. Decay times from time resolved luminescence measurements were compared to the decay times of wet or dry etched mesa wires before and after regrowth. The good optical properties of the GaInAs QWRs are encouraging for future application as a QWR-laser device.     

High-current-gain InGaAs/InP double-heterojunction bipolartransistors grown by metal organic vapor phase epitaxy

By inserting a thin n-InP layer between the p⁺-InGaAs base and the n-InP collector excellent transistor characteristics were obtained. The DE and small-signal current gains were 7000 and 11000, respectively, which are the highest values reported for transistors of this type. The transistors were also operated in a collector-up configuration with DE gains as large as 2500     

Strain status in ZnO film on sapphire substrate with a GaN buffer layer grown by metal-source vapor phase epitaxy

ZnO film of 8 μm thickness was grown on a sapphire (0 0 1) substrate with a GaN buffer layer by a novel growth technique called metal-source vapor phase epitaxy (MVPE). The surface of ZnO film measured by scanning electron microscope (SEM) is smooth and shows many regular hexagonal features. The full width at half maximum (FWHM) of ZnO(0 0 2) and (1 0 2) ω-scan rocking curves are 119 and 202 arcsec, corresponding a high crystal quality. The status of the strain in ZnO thick film was particularly analyzed by X-ray diffraction (XRD) ω-2θ scanning. The results show that the strain in ZnO film is compressive, which is also supported by Raman scattering spectroscopy. The compressive strain can solve the cracking problem in the quick growth of ZnO thick film.     

Adjusting trimethylgallium injection time to explore atomic layer epitaxy of GaAs between 425 and 500°C by organometallic vapor phase epitaxy

In experiments employing a conventional low-pressure, rotating-disk organome-tallic vapor phase epitaxy reactor, GaAs epilayers have been grown at substrate temperatures ranging from 425 to 500°C by exposing the substrate alternately to trimethylgallium (TMG) and AsH₃.The GaAs growth rateR was approximately constant with TMG flow rate, but with increasing TMG injection timet, it increased to more than one monolayer per TMG/AsH₃ cycle without saturating. Although growth was not self-limiting, for one specific combination of temperature andt, a value of R = 1 monolayer/cycle could be achieved by usingt values decreasing from 10.8 s at 425°C to 0.9 s at 500°C in accordance with an Arrhenius relationship between 1/t and absolute temperature.     

Methods for reducing deep level emissions from ZnSe grown by organometallic vapor phase epitaxy

Methods for reducing deep level emission from ZnSe layers grown by photo-assisted organometallic vapor phase epitaxy were studied using photo-luminescence. A number of approaches to achieve reductions in deep level emissions were investigated. One of them was the use of a flow modulation technique. Reduction in the deep level emissions was observed when the layers were annealed under zinc-rich conditions during this growth process. The effect of cadmium as an isoelectronic dopant in ZnSe was also studied. It was observed that “doping” levels of cadmium resulted in considerable reduction in deep level emissions from ZnSe layers. Layers were grown under different II/VI ratios, and compared to cadmium doped layers of similar ratios. Reduction in deep level emissions were observed in all cadmium doped layers. Cadmium, therefore, seems to be the most promising isovalent dopant for reducing the deep level emissions in ZnSe.     

Diffuse diffracted features and ordered domain structures in GalnP layers grown by organometallic vapor phase epitaxy

Transmission electron diffraction (TED) and transmission electron microscope (TEM) studies have been made of organometallic vapor phase epitaxial Ga_xIn_1−xP layers (x ≈ 0.5) grown at temperatures in the range 570–690°C to investigate ordering and ordered domain structures. TED and TEM examination shows that the size and morphology of ordered domains depend on the growth temperature. The ordered domains change from a fine rod-like shape to a plate-like shape as the growth temperature increases. The domains are of width 0.6∼2 nm and of length 1∼10 nm. Characteristic diffuse features observed in TED patterns are found to depend on the growth temperature. Extensive computer simulations show a direct correlation between the ordered domain structures and such diffuse features. A possible model is suggested to describe the temperature dependence of the ordered domain structure.     

Characterization of InP grown by OMVPE using trimethylindium and tertiarybutylphosphine (TBP) at low V/III ratios and reduced TBP partial pressures

We report an OMVPE growth process for InP using trimethylindium (TMI) and tertiarybutylphosphine (TBP), a V/III ratio of 15, and a TBP partial pressure of 0.5 Torr. Growth is initiated with a 0.1 μm buffer layer employing a ramped TBP flow. Results are presented for InP grown with two different samples of both TMI and TBP and compared to previous experimental results and theoretical predictions. Good surface morphology is obtained from 540 to 600° C. The net carrier concentrations, N_d-N_a, decrease with increasing growth temperature—but never fall below 1.3 × 10¹⁶ cm^-3. Mobilities of 3990 and 11200 cm²/V.sec are observed at 300 and 77 K, respectively. At 77 K, we infer a compensation ratio of ∼0.4, independent of N_d-N_a. Photoluminescence measurements at 6 K show intense near bandgap emission with a full width half maximum proportional to N_d-N_a. Weak emission is also observed from carbon acceptors, independent of growth temperature. Secondary ion mass spectroscopy measurements are performed on an InP wafer grown with four different temperatures. The observed sulfur concentration drops from 1 × 10¹⁸ to 6 × 10¹⁶ cm^-3 with increasing growth temperature. This confirms that sulfur is an important residual impurity in TBP. The observed carbon concentration is 4–6 × 10¹⁶ cm^-3, regardless of growth temperature.     

Metalorganic vapor phase epitaxy of InP using the novel P-source ditertiarybutyl phosphine (DitBuPH)

In this study, the use of a novel phosphorous precursor for low pressure metalorganic vapor phase epitaxy (LP-MOVPE) application has been investigated. Ditertiarybutyl phosphine ((C₄H₉)₂-P-H, DitBuPH) as substitute for the standardly used hydrid gas phosphine (PH₃) promises apart from strongly reduced toxicity due to the reduction of P-H bonds, an enhancement in cracking efficiency as well as a reduction in growth temperature. Layer quality has been examined by means of optical and scanning electron microscopy (SEM), temperature-dependent van der Pauw Hall as well as photoluminescence (PL) measurements. Uncompensated n-type InP-layers (1.0 x 1.5 cm^-3; 59600 cm²Vs)^-1 at 77K) are realized using DitBuPH in combination with commercial TMIn. All results are compared with those obtained by using PH₃ and commercial tertiarybutyl phosphine (TBP) as P-source, respectively.     

Germanium as a deep level in alxga1− xas grown by organometallic vapor phase epitaxy

Optoelectronic devices require materials which exhibit extremely low trap concentrations. The Al_xGa_1−xAs system has been used extensively for optoelectronic applications despite trap concentrations in the Al_xGa_1−xAs which limit the efficiency of the resulting devices. Deep level transient spectroscopy (DLTS) performed on Al_0.2Ga_0.8As layers grown by organometallic vapor phase epitaxy (OMVPE) has revealed three traps with concentrations >10¹³ cm⁻³ -E _c-E_t = 0.3, 0.5 and 0.7 eV. The dominant source of the 0.3 eV trap has proven to be a Ge impurity in arsine. SIMS analysis of Al_0.2Ga_0.8As samples show Ge as the only candidate for the impurity responsible for the 0.3 eV trap. DLTS and SIMS analysis performed on Al_0.2Ga_0.8As samples intentionally doped with Ge displayed a proportional increase in the 0.3 eV trap concentration with the Ge concentration and establishes that Ge is indeed the source of the 0.3 eV trap in Al_xGa_1−xAs. Comparison of C-V, SIMS and DLTS measurements performed on Al_xGa_1-xAs:Ge indicate that approximately 30% of elemental Ge incorporated created the 0.3 eV trap, DX_Ge.     

Structural study of GaN grown on (001) GaAs by organometallic vapor phase epitaxy

Detailed transmission electron microscope (TEM) and transmission electron diffraction (TED) examination has been performed on organometallic vapor phase epitaxial GaN layers grown on (001) GaAs substrate to investigate microstructures and phase stability. TED and TEM results exhibit the occurrence of a mixed phase of GaN. The wurtzite (α) phase grains are embedded in the zinc-blende (β) phase matrix. It is shown that there are two types of the wurtzite GaN phase, namely, the epitaxial wurtzite and the tilted wurtzite. The tilted wurtzite grains are rotated some degrees ranging from ∼5° to ∼35° regarding the GaAs substrate. A simple model is presented to describe the occurrence of the mixed phases and the two types of the wurtzite phase.