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We describe the metal-organic chemical vapor deposition (MOCVD) growth of InAsSb/InAs and GaAsSb/GaAs(P) multiple quantum well (MQW) and InAsSb/InAsP and InAsSb/InPSb strained-layer superlattice (SLS) active regions for use in mid-infrared emitters. We also describe the growth and initial characterization of GaAsSbN/GaAs MQW structures. By changing the layer thickness and composition of the InAsSb SLSs and MQWs, we have prepared structures with low temperature (

We have investigated deep levels in 1.05 eV, Sn-doped, n-type In0.075Ga0.925As0.975N0.025 lattice-matched to GaAs. The samples were grown by metal–organic chemical vapor deposition. Capacitance–voltage measurements were used to determine the electron concentration in both as-grown and postgrowth annealed samples, and a decrease in net electron concentration of about 1.5×1017 cm−3 was observed following annealing. Deep level transient spectroscopy measurements are consistent with the presence of four majority-carrier electron traps, E1 (a broad distribution extending from the conduction band edge to approximately EC−0.2 eV), E2(0.36 eV), E3(0.34 eV), and E4(0.82 eV), as well as one minority-carrier hole trap, H1(0.71 eV), in our material. It is shown that E2 and H1, both of which are present in the annealed material only, are likely the same defect observed under conditions of electron and hole emission, respectively. Current–voltage-temperature measurements indicate a thermal activation energy of 0.35 eV ...

The surface morphology of GaAs films grown on offcut Ge substrates is studied using a scanning force microscope (SFM). We investigated the effects of the Ge buffer layer, growth temperature, film thickness, and prelayer on the GaAs surface morphology. The starting Ge substrates are offcut 6° toward the [110] direction to minimize single steps on the substrates before molecular beam epitaxial film growth. We find that comparing with GaAs samples grown without Ge buffer layers or with unannealed Ge buffer layers, samples with annealed Ge buffer layers are much smoother and contain no antiphase boundaries (APBs) on the surface. For thick (≥1 µm) GaAs films with an annealed Ge buffer layer, the surfaces display crosshatch lines and elongated mounds (along \([\bar 110]\), which are associated with the substrate offcut direction. As the film thickness increases, the crosshatch lines become shorter, denser and rougher, and the mounds grow bigger (an indication of GaAs homoepitaxial growth). We conclude that annealed Ge buffer layers are crucial for growing high quality GaAs films with few APBs generated during the growth. In addition, under optimal conditions, different prelayers make little difference for thick GaAs films with annealed Ge buffer layers.

The nucleation and growth of GaAs films on offcut (001) Ge wafers by solid source molecular beam epitaxy (MBE) is investigated, with the objective of establishing nucleation conditions which reproducibly yield GaAs films which are free of antiphase domains (APDs) and which have suppressed Ge outdiffusion into the GaAs layer. The nucleation process is monitored by in-situ reflection high energy electron diffraction and Auger electron spectroscopy. Several nucleation variables are studied, including the state of the initial Ge surface (single-domain 2×1 or mixed-domain 2×1:1×2), the initial prelayer (As, Ga, or mixed), and the initial GaAs growth temperature (350 or 500°C). Conditions are identified which simultaneously produce APD-free GaAs layers several microns in thickness on Ge wafers with undetectable Ge outdiffusion and with surface roughness equivalent to that of GaAs/GaAs homoepitaxy. APD-free material is obtained using either As or Ga nucleation layers, with the GaAs domain dependent upon the initial exposure chemical species. Key growth steps for APD-free GaAs/Ge growth by solid source MBE include an epitaxial Ge buffer deposited in the MBE chamber to bury carbon contamination from the underlying Ge wafer, an anneal of the Ge buffer at 640°C to generate a predominantly double atomic-height stepped surface, and nucleation of GaAs growth by a ten monolayer migration enhanced epitaxy step initiated with either pure As or Ga. We identify this last step as being responsible for blocking Ge outdiffusion to below 1015 cm−3 within 0.5 microns of the GaAs/Ge interface.

Large substrate surface temperature decreases are observed during molecular beam epitaxy growth onto small indium bonded substrates, due to coating of the molybdenum block. These large temperature transients, along with other difficulties associated with indium bonding (e.g., potential substrate surface damage, unwanted indium on the back of the substrate) make indium free substrate mounting desirable, however, indium free mounting systems have previously been restricted to whole standard‐sized round wafers. In this study we compare the temperature characteristics of new indium free modular substrate mounting blocks, which can accommodate substrates of various sizes (up to 3 inch diameter) and shapes, with traditional indium mounting of small substrates. Although the new modular indium free holders have a large molybdenum surface area exposed to the molecular beams, we find that the substrate surface temperature transients during growth are reduced to nearly negligible levels versus similar growth on indi...

The effects of reabsorption and band‐gap narrowing (BGN) on experimental photoluminescence (PL) spectra of n‐InP grown by metalorganic chemical vapor deposition are analyzed. PL spectra show a pronounced widening of the main PL peak and a shift of that peak to higher photon energy with increasing doping due to band filling. However, the magnitude of these effects, both here and in earlier studies of n‐type III–V semiconductors, is smaller than expected based upon band filling calculations and electrical measurements. Various explanations for these discrepancies between PL spectra and band filling calculations have been proposed, but little experimental support is currently available. In this article we demonstrate unambiguously that both the n‐InP PL peak width and the peak position are significantly reduced by reabsorption, and that reabsorption completely explains the observed discrepancy between the measured PL peak width and the calculated band filling based on electrical measurements. In particular, ...

To gain insight into the nitrogen-related defects of InGaAsN, nitrogen vibrational mode spectra, Hall mobilities, and minority carrier diffusion lengths are examined for InGaAsN (1.1 eV band gap) grown by molecular beam epitaxy (MBE). Annealing promotes the formation of In–N bonding, and lateral carrier transport is limited by large scale (≫mean free path) material inhomogeneities. Comparing solar cell quantum efficiencies with our earlier results for devices grown by metalorganic chemical vapor deposition (MOCVD), we find significant electron diffusion in the MBE material (reversed from the hole diffusion in MOCVD material), and minority carrier diffusion in InGaAsN cannot be explained by a “universal,” nitrogen-related defect.

Spectroscopic ellipsometry (SE) characterization of several complex Si (sub X)Ge (sub 1-x)/Si heterostructures prepared for device fabrication, including structures for heterojunction bipolar transistors (HBT), p-type and n-type heterostructure modulation doped field effect transistors, has been performed. We have shown that SE can simultaneously determine all active layer thicknesses, Si (sub X)Ge (sub 1-x) compositions, and the oxide overlayer thickness, with only a general knowledge of the structure topology needed a priori. The characterization of HBT material included the SE analysis of a Si (sub X)Ge (sub 1-x) layer deeply buried (600 nanometers) under the silicon emitter and cap layers. In the SE analysis of n-type heterostructures, we examined for the first time a silicon layer under tensile strain. We found that an excellent fit can be obtained using optical constants of unstrained silicon to represent the strained silicon conduction layer. We also used SE to measure lateral sample homogeneity, providing quantitative identification of the inhomogeneous layer. Surface overlayers resulting from prior sample processing were also detected and measured quantitatively. These results should allow SE to be used extensively as a non-destructive means of characterizing Si (sub X)Ge (sub 1-x)/Si heterostructures prior to device fabrication and testing.

An ellipsometric study of ambient‐reaction‐produced BaCO3 overlayer growth on laser‐ablated YBa2Cu3O7−x is presented as a function of time. The effects of the anisotropy of YBa2Cu3O7−x on the ellipsometric data inversion process are discussed, and it is concluded that with certain restrictions on the data acquisition method, the anisotropic substrate can be adequately modeled by its isotropic pseudodielectric function for the purpose of overlayer thickness estimation. It is found that after an initial period of rapid growth attributed to the chemical reaction of the exposed surface bonds, the BaCO3 overlayer growth is linear at 1–2 A per day. This slow growth rate is attributed to the complexity of the BaCO3 forming reaction, together with the need for ambient reactants to diffuse through the overlayer.

An ellipsometric study of MOCVD-grown layers of AlGaAs and InGaAs in thick films and strained layer complex structures is presented. It is concluded that the ternary composition of thick nonstrained layers can be accurately determined to within experimental errors using numerical algorithms. In the case of complex structures, thickness of all layers and the alloy composition of nonstrained layers can be determined simultaneously, provided that the correlations between parameters is no higher than 0.9.

Due to the large size and the number of diffusion pumps, space simulation chambers cannot be easily calibrated by the usual test dome method for measuring backstreaming from oil diffusion pumps. In addition, location dependent contamination may be an important parameter of the test. The backstreaming contamination was measured in the Space Power Facility (SPF) near Sandusky, OH, the largest space simulation vacuum test chamber in the U.S.. Small clean silicon wafers placed at all desired measurement sites were used as contamination sensors. The facility used diffusion pumps with DC 705 oil. The thickness of the contamination oil film was measured using ellipsometry. Since the oil did not wet the silicon substrate uniformly, two analysis models were developed to measure the oil film: (1) continuous, homogeneous film; and (2) islands of oil with the islands varying in coverage fraction and height. In both cases, the contamination film refractive index was assumed to be that of DC 705. The second model improved the ellipsometric analysis quality parameter by up to two orders of magnitude, especially for the low coverage cases. Comparison of the two models shows that the continuous film model overestimates the oil volume by less than 50 percent. Absolute numbers for backstreaming are in good agreement with published results for diffusion pumps. Good agreement was also found between the ellipsometric results and measurements done by x-ray photoelectron spectroscopy (XPS) and by scanning electron microscopy (SEM) on examples exposed to the same vacuum runs.

Electron and hole transport in compensated, InGaAsN ({approx} 2% N) are examined through Hall mobility, photoconductivity, and solar cell photoresponse measurements. Short minority carrier diffusion lengths, photoconductive-response spectra, and doping dependent, thermally activated Hall mobilities reveal a broad distribution of localized states. At this stage of development, lateral carrier transport appears to be limited by large scale (>> mean free path) material inhomogeneities, not a random alloy-induced mobility edge.

By employing a reactive low-temperature wafer bonding technique, we have demonstrated oxide-defined 850 nm vertical-cavity surface-emitting lasers (VCSEL's) on Si substrates. Devices reach a differential quantum efficiency of 53% and a light output power of 7.1 mW under room temperature and continuous-wave operation without a heat sink.

Variable-angle spectroscopic ellipsometry was used to estimate the thickness of all layers within the optical penetration depth of InGaAs-based modulation doped field effect transistor structures. Strained and unstrained InGaAs channels were made by molecular beam epitaxy (MBE) on InP substrates and by metal-organic chemical vapor deposition on GaAs substrates. In most cases, ellipsometrically determined thickness were within 10% of the growth-calibration results. The MBE-made InGaAs strained layers showed large strain effects, indicating a probable shift in the critical points of their dielectric function toward the InP lattice-matched concentration.

Topographic changes and surface contact potential variations near defects on the surface of AlGaAs/GaAs double heterojunction structures grown on Ge substrates are studied using scanning force microscope and electrostatic force microscope. Comparison with transmission electron microscopy results indicates that these surface defects are directly related to stacking faults originated from the GaAs/Ge interface. The surface contact potential inhomogeneities near these defects are consistent with variations in Si dopant concentration.

A high bulk minority-carrier lifetime in GaAs grown on Si-based substrates is demonstrated. This was achieved by utilizing a step-graded Ge/GeSi buffer (threading dislocation density 2×106 cm−2) grown on an offcut (001) Si wafer, coupled with monolayer-scale control of the GaAs nucleation to suppress antiphase domains. Bulk minority-carrier lifetimes (τp) were measured using room-temperature time-resolved photoluminescence applied to a series of Al0.3Ga0.7As/GaAs/Al0.3Ga0.7As double-heterojunction structures doped n=1.1×1017 cm−3 with GaAs thicknesses of 0.5, 1.0, and 1.5 μm. A lifetime τp=7.7 ns was determined for GaAs grown on Si. The extracted interface recombination velocity of 3.9×103 cm/s is comparable to recombination velocities found for Al0.3Ga0.7As/GaAs interfaces grown on both GaAs and Ge wafers, indicating that the crosshatch surface morphology characteristic of strain-relaxed Ge/GeSi surfaces does not impede the formation of high-electronic-quality interfaces. These results hold great promise...

Vertical-cavity lasers emitting at 1.3 /spl mu/m are extremely attractive for high bandwidth fiber communications where it is advantageous to operate at the dispersion minimum of silica optical fiber. To date, VCSELs based on pseudomorphic GaAs materials have achieved lasing emission only slightly longer than 1.3 /spl mu/m. We report the first 1.3 /spl mu/m selectively oxidized VCSELs using InGaAsN quantum wells which operate at continuous wave at and above room temperature.

Heteroepitaxial InP films grown on GaAs substrates by metalorganic chemical vapor deposition are demonstrated to have a higher concentration of zinc occupying interstitial sites than do equivalent homoepitaxial InP layers. A zinc interstitial‐related donor‐to‐acceptor photoluminescence peak is observed in heteroepitaxial InP films which is absent in the homoepitaxial sample spectra. Capacitance–voltage measurements yield a lower hole concentration in the heteroepitaxial layers versus the homoepitaxial layers, which is attributable to a higher fraction of zinc in interstitial sites within the heteroepitaxial layers. Additionally, the hole concentration of the heteroepitaxial layers is found to be lower near the heterojunction as compared with the film surface region, correlating with a higher dislocation density near the heterojunction as seen by transmission electron microscopy. We conclude that the increased zinc interstitial concentration and the reduced hole concentration are due to dislocation‐zinc so...

Plasma hydrogenation has recently been demonstrated to be highly effective in passivating dislocations in heteroepitaxial InP and is a promising technique for achieving viable heteroepitaxial InP solar cells. In this paper, the effects of hydrogen on the fundamental properties of three dislocation related hole traps in heteroepitaxial InP/GaAs are presented. Hydrogen passivation significantly alters the dislocation trapping kinetics, causing point defect-like behavior consistent with a transformation from dislocation-related defect bands within the InP bandgap to a low concentration of individual deep levels after hydrogenation. Furthermore, hydrogen passivation is shown to shift the dominant space charge generation center from E/sub c/-0.71 eV to E/sub c/-0.92 eV, away from midgap. A model is proposed which explains these effects on the basis of decreased electronic interaction between dislocation sites. Finally, a comparison of InP material quality grown on GaAs, Ge and GaAs/Ge substrates is presented, and hydrogen passivation of InP/GaAs/Ge structures is reported.

Elimination of anti-phase domains (APDs), threading dislocations and uncontrolled interface diffusion are critical considerations for achieving maximum design flexibility and high efficiency in multi-bandgap III-V solar cells on Ge. In this paper, we identify critical growth steps to eliminate each of these problems and present an optimum molecular beam epitaxy (MBE) growth procedure which yields APD-free, near-dislocation-free GaAs/Ge with greatly suppressed interdiffusion in both the GaAs overlayer and Ge substrate. For solid source MBE, elimination of APDs requires a double-stepped, clean Ge surface and a prelayer consisting of a complete monolayer of either As or Ga. Correct conditions can be observed and maintained by real-time in-situ monitoring to ensure reproducibility. Initiating growth at low temperature with migration enhanced epitaxy virtually eliminates Ge diffusion into GaAs and Ga diffusion into Ge, while As diffusion into Ge is substantially suppressed.

We present an ellipsometric study of two Si(0.5)Ge(0.5)/Si strained-layer superlattices grown by MBE at low temperature (500 C), and compare our results with X-ray diffraction (XRD) estimates. Excellent agreement is obtained between target values, XRD, and ellipsometry when one of two available Si(x)Ge(1-x) databases is used. We show that ellipsometry can be used to nondestructively determine the number of superlattice periods, layer thicknesses, Si(x)Ge(1-x) composition, and oxide thickness without resorting to additional sources of information. We also note that we do not observe any strain effect on the E1 critical point.

The dielectric function of a thick layer of In(0.52)Al(0.48)As lattice matched to InP was measured by variable angle spectroscopic ellipsometry in the range 1.9-4.1 eV. The In(0.52)Al(0.48)As was protected from oxidation using a thin In(0.53)Ga(0.47)As cap that was mathematically removed for the dielectric function estimate. The In(0.52)Al(0.48)As dielectric function was then verified by ellipsometric measurements of other In(0.53)Ga(0.47)As/In(0.52)Al(0.48)As structures, including (MODFET), and is shown to provide accurate structure layer thicknesses.

are being developed as laser active regions. By introducing GaAsP layers into the active region for strain-compensation, gain can be increased using multiple InGaAsN quantum wells. In this work, we report the first strain-compensated, 1 .3 jim InGaAsN MQW lasers. Our devices were grown by metal-organic chemical vapor deposition.Lasers with InGaAsN quantum well active regions are proving superior to lasers constructed with competing active regionmaterials. Under pulsed operation, our 1.3 im InGaAsN lasers displayed negligible blue-shift from the low-injection LEDemission, and state-of-the-art characteristic temperature (1 59

Nitrogen vibrational mode spectra, Hall mobilities, and minority carrier diffusion lengths are examined for InGaAsN (≈ 1.1 eV bandgap) grown by molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD). Independent of growth technique, annealing promotes the formation of In-N bonding, and lateral carrier transport is limited by large scale (Ęmean free path ) material inhomogeneities. Comparing solar cell quantum efficiencies for devices grown by MBE and MOCVD, we find significant electron diffusion in the MBE material (reversed from the hole diffusion occurring in MOCVD material), and minority carrier diffusion in InGaAsN cannot be explained by a “universal”, nitrogen-related defect.

The variation of the value of the linewidth of an excitonic transition in InGaAsN alloys (1% and 2% nitrogen) as a function of hydrostatic pressure using photoluminescence spectroscopy is studied at 4K. The excitonic linewidth increases as a function of pressure until about 100 kbar after which it tends to saturate. This pressure dependent excitonic linewidth is used to derive the pressure variation of the exciton reduced mass using a theoretical formalism based on the premise that the broadening of the excitonic transition is caused primarily by compositional fluctuations in a completely disordered alloy. The linewidth derived ambient pressure masses are compared and found to be in agreement with other mass measurements. The variation of this derived mass is compared with the results from a nearly first-principles approach in which calculations based on the local density approximation to the Kohn-Sham density functional theory are corrected using a small amount of experimental input.

The realization of monolithic optical interconnects by integration of III-V materials with conventional Si circuitry has long been hindered by materials incompatibilities (i.e. lattice mismatch and heterovalent interface) and practical processing constraints. We have demonstrated successful integration of hetero-epitaxially grown InGaAs/Si diodes with an n-well CMOS process on (001) Si offcut 6 degrees towards [110]. The In0.15Ga0.85As/InxGa1- xAs/GaAs/Si diodes were grown by atmospheric pressure organo-metallic chemical vapor deposition (OMCVD) and features a room temperature R0A product of 20,000 ohm-cm2. No degradation of PMOS or NMOS transistor characteristics was detected upon integration of the III-V devices. Further improvement of III-V/Si device characteristics are anticipated in future efforts by incorporating relaxed, compositionally- graded Ge/GexSi1-x/Si with low threading dislocation densities (approximately 2 X 106/cm2) to bridge the gap in lattice constants between Si and GaAs. Recent progress towards this end includes the suppression of antiphase disorder during GaAs growth on Ge/GexSi1-x/Si by OMCVD and strong room temperature photoluminescence from In0.20Ga0.80As QW test structures on GaAs/GexSi1- x/Si at 920 nm.

The bandgap of InP is near ideal for the high theoretical conversion efficiency of the air mass zero (AM0) light spectrum experienced in space. This combined with the well known radiation resistance makes InP an ideal candidate for space solar cell use. The p/n configuration has several advantages over the n/p configuration, however, the conversion efficiency of p/n InP cells has been low compared to the n/p configuration, mostly do to poor performance of the Zn doped emitter. We have recently achieved a 17.6% AMO conversion efficiency for a p/n InP cell on an InP substrate and have achieved this record efficiency through understanding of the role of Zn interstitial defects and the hydrogen interactions with these defects. The effect of the Zn defect on device performance will be described.

Deep levels in MOCVD grown p-InP on GaAs substrates have been investigated by Deep Level Transient Spectroscopy (DLTS). The effect of hydrogenation on the electrical activity of these levels has been studied through a combination of DLTS and Photoluminescence (PL) measurements. DLTS measurements indicate a drop of trap density from σ 5 × 1014 cm−3 to σ 1 × 1012 cm−3 after hydrogenation. Annealing at 400°C reactivated only the dopants, while temperatures above 600°C were necessary for deep-level reactivation. This combined with a logarithmic dependence on fill pulse time, indicate that at least one broad DLTS peak is associated with dislocations. The PL the DLTS results show that the dislocation related traps are passivated by hydrogen, preferentially over the dopants and that a wide annealing window exists for dopant reactivation.

Selectively oxidized vertical cavity lasers emitting at 1294 nm using InGaAsN quantum wells are reported for the first time which operate continuous wave at and above room temperature. The lasers employ two n-type Al{sub 0.94}Ga{sub 0.06}As/GaAs distributed Bragg reflectors each with a selectively oxidized current aperture adjacent to the optical cavity, and the top output mirror contains a tunnel junction to inject holes into the active region. Continuous wave single mode lasing is observed up to 55 C. These lasers exhibit the longest wavelength reported to date for vertical cavity surface emitting lasers grown on GaAs substrates.

The epitaxial growth of GaAs on Si substrates through the use of a Ge/graded Si1−xGex/Si buffer layer would allow monolithic integration of GaAs-based opto-electronics with Si microelectronics. As an initial step toward this goal, this study examines factors which influence the quality of GaAs growth by molecular beam epitaxy (MBE) on bulk Ge substrates. Key findings include the need for an epitaxial Ge smoothing cap deposited in the MBE chamber, the significant detrimental effect of As overpressure on the resultant GaAs crystalline quality, and the efficiency of a very thin (∼3 nm) migration enhanced epitaxy (MEE) nucleation layer at suppressing both anti-phase domain (APD) formation and interdiffusion across the GaAs/Ge heterointerface. Using this developed optimized growth process, APD-free GaAs on Ge is obtained which has undetectable Ga and Ge cross-diffusion, and As diffusion into the substrate at ⩽1×1018 cm−3. Preliminary results for growths on Ge/Si1−xGex/Si substrates are also presented.

Pyrometric interferometry (PI) is becoming a widely used method of obtaining in situgrowth rates of GaAs and AlAs epitaxial layers grown by molecular beam epitaxy, due to its use of the ubiquitous narrow‐band pyrometer and its ability to measure growth rates on rotating substrates. However, the extension of this technique to Al x Ga1−x As has been hindered by the lack of a convenient, detailed oscillation period calibration curve for the technologically important aluminum composition range 0.0

Ellipsometric measurements on plasma deposited “diamondlike” amorphous carbon (a-C:H) films were taken in the visible, (E = 1.75 to 3.5 eV). The films were deposited on Si and their properties were varied using high temperature (up to 750 °C) anneals. The real (n) and imaginary (k) parts of the complex index of refraction N were obtained simultaneously. Following the theory of Forouhi and Bloomer (Phys. Rev. B34, 7018 (1986)), a least squares fit was used to find the dispersion relations n(E) and k(E). Reasonably good fits were obtained, showing that the theory can be used for a-C:H films. Morever, the value of the energy gap Eg obtained in this way was compared to the Eg value using conventional Tauc plots and reasonably good agreement was obtained.