High quality InSb epilayers were grown on GaAs substrates by metal organic chemical vapor deposition using a two-step growth procedure involving trimethal indium (TMIn) predeposition. From transmission electron microscopy studies, we found that an interdiffusion layer of thickness of 10 Å forms at the interface when the substrate is exposed to TMIn for approximately 6 secs prior to the growth of the InSb filns. Hall mobilities up to σ 52,000 cm2/V-s were obtained at 300 K on a 2.1-μm-thick InSb heteroepitaxial film. In contrast, samples without TMIn predeposition showed polycrystallinity of the InSb films grown on single crystalline GaAs substrates. The effect. of TMNIn predeposition is to minimize the misorientation of the grains, suppress the polycrystallinity, decrease the density of threading dislocations, and increase the electron mobilities in the films. However, we found that too much TMIn predeposition gives rise t.o an intermixing layer at the InSb/GaAs interface which deteriorates the film quality. Details of the effect of the TMIn predeposition on the microstructure of InSb/GaAs with different predeposition times (zero, 6, and 12 secs) are discussed.

Germanium films were deposited on GaAs (100) substrates at temperatures between room temperature (RT) and 500°C using ultra high vacuum (UHV) E-beam and sputtering deposition methods. The Ge film deposited in UHV at 100°C was amorphous and had a flat absorbance curve over the range investigated, 4000 - 500 cm-1, with a value of 0.03 at 1000 cm1 (10μm). Films deposited by E-beam at RT and 50°C had comparably low absorbances, but they contained a peak at 830 cm-1, which was possibly due to absorption by a Ge-O bond. The amorphous film deposited at 150°C and the single crystal films deposited at 400 and 500°C by E-beam had larger absorbances caused by free carrier absorption. The amorphous Ge sputtered film deposited at RT had a relatively low absorbance, but it contained the absorption peak attributed to Ge-O. The absorbance increased dramatically when it was annealed at 400 or 500°C due to the rapid out diffusion of Ga and As through the relatively open structure.

The growth of I1/VI epitaxial layers by molecular beam epitaxy (MBE) for blue/green lasers is described. To elucidate the issues in the growth of II/VI materials, the differences between II/V and II/VI MBE growth are addressed, including factors such as: substrates, molecular beam sources, lattice matching, sticking coefficients, and surface diffusion. Results of reflection high-energy diffraction (RHEED) oscillation measurements are presented. RHEED oscillations have proven to be a valuable in-situ tool for controlling certain aspects of 1I/VI MBE growth, such as ZnSySe1-y composition, Zn1-xMgxSe composition, and the growth rate of ZnSe during migration-enhanced epitaxy.

We have obtained continuous-wave laser operation at room temperature from a (Zn,Mg)(S,Se)-based Il-VI separate-confinement heterostructure where injection of holes into the p-type quaternary was achieved through the employment of a Zn(Se,Te) graded-bandgap contact. The laser devices exhibit threshold current densities of below 300 A/cm2 and voltages below 6 V. Issues related to the control of the growth of the quaternary (Zn,Mg)(S,Se) compound, and a proposal to further reducing the laser operating voltage will also be described.

Nitrogen and helium mixed gas plasma was used to grow p-ZnSe. Using the mixed gas, the acceptor concentration could be controlled from 6x1016 to 7x1017 cm−3 while films doped using the nitrogen plasma exhibited the acceptor concentration of 3x1017 cm−3. Doping characteristics such as the acceptor concentration and the PL properties depend on the gas mixing ratio and the rf power. Plasma spectroscopy was used to characterize the variety of the species in the plasma. Although the variety of the nitrogen related peaks in the spectrum were not significantly affected by the gas mixing, several peaks (for example 745nm and 825nm) showed intensity variation that was similar to the acceptor concentration variation with respect to the N2 and He gas mixing ratio.

We first present the nitrogen location on radical nitrogen doped ZnSe-MBE surface studied by ISARS(Ion Scattering And Recoiling Spectrometry). In the recoiling nitrogen measurements of heavy doped ZnSe:N surface, a two-peak structure is observed corresponding to two recoil processes, i.e., direct recoil (DR) and surface recoil(SR). DR events occur due to the singlecollision recoiling from Se site nitrogen. On the other hand, SR events occur due to the nitrogen recoiling scattered by second layers and is highly sensitive to the nitrogen location on ZnSe:N surface during MBE growth. The experimental results and calculation suggest that the optimum doped nitrogen atoms locate in the substitutional Se sites but excess nitrogen atoms locate in the interstitial sites.

High quality ZnSe:Cl has been grown on GaAs by gas source molecular beam epitaxy (GSMBE); elemental Zn and H2Se are used as source materials, with ZnCl2 as a dopant source for donors. Atomic Cl concentrations ([Cl]) approaching 1020 cm−3 have been incorporated into the lattice as indicated by secondary ion mass spectrometry (SIMS). At incorporation levels greater than 1020 cm−3, an appreciable decrease in the growth rate has been observed. The sharp transition to a negligible growth rate is attributed to the occurrence of a surface chemical reaction originating from Cl and H which are present in the GSMBE environment. For [Cl] as high as 4 x 1018 cm−3, the films exhibited high crystalline quality, as indicated by photoluminescence originating from a single intense donor-bound excitonic transition. Hydrogenation of semiconductors can potentially result in the electrical passivation of incorporated acceptor and donor species. In the case of ZnSe:Cl, H was present in the ZnSe layers, but did not appear to adversely affect the electrical properties of the n-type films. In contrast, for the growth of ZnSe:N, where a nitrogen plasma cell was employed as a source of nitrogen, the H concentration (as determined by SIMS) was observed to track the N concentration. The ZnSe:N films were highly resistive for various amounts of N incorporation, which suggests that H incorporation is an issue of primary importance in the p-type doping of ZnSe grown by GSMBE.

ZnS, ZnSe, CdS and CdSe thin films were grown on InP or GaAs substrates with high ptype and n-type doping concentrations by pulsed excimer laser deposition without any postannealing processing. The x-ray diffraction results showed that these thin films were fully epitaxial (in-plane aligned). These high quality films are suitable for use as optoelectronic devices which will operate in the visible region of the spectrum.

We designed a plasma cell for nitrogen doping of ZnSe, using a metal organic vapour phase epitaxy (MOVPE) horizontal reactor. With the following growth conditions: Tg=300°C, P=1 Torr and a molar VI/II ratio of 5, successful p-type doping was obtained, as assessed by photoluminescence experiments, but with a free carrier concentration still too low to be detected by transport measurements. The passivation of nitrogen active species by hydrogen is discussed. The possible interaction with the carrier gas has been studied through the use of H2, N2 and He as carrier gases. We demonstrate that the use of helium as carrier gas leads to sensible improvement of the photoluminescence features related to nitrogen acceptor. On the other hand, the use of N2 as carrier gas leads to poor homogeneity of the layers with few effects on the doping level.

ZnTe has gained attention as a promising material for short wavelength optoelectronic applications. Unlike ZnSe, ZnTe can be doped p-type but not n-type. There are few reports detailing the growth and doping of ZnTe films through the MOVPE technique. We present growth and doping studies for ZnTe formed through low pressure MOVPE. Dimethylzinctriethylamine and diisopropyltelluride were chosen as the metalorganic precursors. Growth studies were carried out on both GaAs (100) and GaSb (100) substrates. Growth morphology was very sensitive to both the lattice mismatch and the initial surface preparation. This is particularly evident on the GaSb substrates. ZnTe growth temperatures ranged from 340 to 420°C, and growth rates of up to 1 μm/hour were achieved. ZnTe was found to be readily doped using tertiarybutylphosphine, with p-type concentrations ranging from 4×1016 cm−3 to 2x1019 cm−3, and corresponding room temperature hole mobilities between 55 and 12 cm2/V-sec. Tertiarybutylphosphine was also observed to significantly improve the surface morphology for growths on GaSb substrates.

The thermal expansion behavior of ZnSe and ZnS0.03Se0.97 epilayers grown on GaAs has been investigated using high resolution X-ray diffraction at temperatures between room temperature and the growth temperature. The lattice parameters perpendicular and parallel to the surface were measured with the Bond's method. The lattice mismatch for a partially relaxed ZnSe layer was Δa(⊥)/a =2300 ppm and Δa(‖)/a = 2600 ppm at room temperature(R.T.) and Δa (⊥)/a =3600 ppm and Δa(‖)/a =2400 ppm at 250°C. For ZnS0.03Se0.97 which is almost lattice matched at R.T. to GaAs, Δa(⊥)/a =200 ppm, Δa(⊥)/a =20ppmatR.T. and Δa(⊥)/a =1400ppm, Δa(⊥)/a =50ppm at 250°C. The relaxed lattice constants were evaluated and the thermal expansion coefficients of relaxed ZnSe layers were found to vary from 7.8*10−6/°C at room temperature to 12.2*10−6/°C at 250°C and for ZnS0.03Se0.97 layers the variation was from 7.5*10−6/°C at R.T. to 11.7*10−6/°C at 250°C.

We have studied the structural properties of MBE-grown ZnSe/GaAs and ZnSTe/GaAs heterostructures using high resolution X-ray diffraction (HRXRD). The transition from pseudomorphic to partially and then fully relaxed strained layers is observed as a function of ZnSe layer thickness. The critical thickness for the on-set of strained relaxation for ZnSe on GaAs(001) is determined to be between 1600 and 1850 Å. Using a simulation program based on the dynamical theory, the poisson's ratio of ZnSe is accurately determined to be v=0.380±0.002. A set of ZnSl-xTex epilayers with 0 ≤ × ≤ 1 was grown on GaAs by MBE for the first time. A linear dependence of the lattice constant upon Te composition is found, which agrees well with the Vegard's Law. The characteristic behaviors of inclination between the layer and substrate planes as a function of layer thickness has been studied on both ZnSe/GaAs and ZnSTe/GaAs systems. The atomic planes of both ZnSe and ZnSTe layers are observed to tilt from those of the GaAs substrate.

Studies of the structure and electrical properties of regular and irregular misfit dislocations in undoped and N-doped ZnSe epilayers grown on GaAs(001) substrates by transmission electron microscopy (TEM), cathodoluminescence (CL) are reported. In undoped ZnSe epilayers, two sets of misfit dislocation arrays were observed: a straight orthogonal array along [110] and, and an irregular array roughly along [100] and [010] directions. The CL observations suggest that the irregular dislocations trap carriers more efficiently than the dislocations along <110>, possibly due to the high density of kinks existing along the zig-zag irregular dislocations. These irregular dislocations can be eliminated by doping nitrogen in the ZnSe epilayer with [N]≥l×1018 cm−3.

The wide bandgap semiconductor ZnSe has been nucleated on epitaxial (In,Ga)P buffer layers (on GaAs substrates) having various In compositions, and hence various lattice constants. The III-V ternary alloy offers a wide range of lattice constants for the heteroepitaxy of a multitude of potential II-VI light emitting devices, such as blue pn injection lasers composed of the (Zn,Mg)(S,Se) material system. Since the II-VI and III-V layers are grown using gas source molecular beam epitaxy in separate dedicated reactors, the technique of amorphous As deposition is employed to passivate the (In,Ga)P surface prior to the ex situ transfer. High resolution double crystal x-ray diffraction measurements on the ZnSe/(In,Ga)P/GaAs heterostructures indicate that for In compositions of 50-52%, the buffer layers with a thickness of 4 μm were only partially relaxed on the GaAs substrates, with the residual mismatch remaining at the ZnSe/III-V heterointerface. The critical thickness of (In,Ga)P, with In concentrations near 52-56%, on GaAs greatly exceeds the predicted critical thickness from either the energy balancing or force balancing model. For an In composition of 56% (and a film thickness of 4 μm), the buffer layers contain an in-plane lattice constant equal to that of ZnSe, and therefore represent the lattice-matched condition, even though the film is not fully relaxed. For (In,Ga)P buffer layers lattice-matched to ZnSe, but mismatched to GaAs, the surface exhibits the expected cross-hatched surface morphology. The occurrence of the cross-hatched surface is significantly alleviated by the addition of a pseudomorphic layer of GaAs positioned between the ZnSe and (In,Ga)P layer.

High-quality ZnSe epilayers on GaAs substrates have been grown by MOCVD. Diethylzinc (DEZn) and diethylselenide (DESe) were used as source materials. Growth studies were done at 400°C under different growth conditions in an atmospheric pressure MOCVD reactor. The as-grown ZnSe epilayers were characterized by a wide variety of techniques, such as double crystal x-ray diffraction, low-temperature photoluminescence (PL), transmission electron microscopy (TEM), secondary ion mass spectrometry (SIMS), and scanning electron microscopy (SEM).

The results show excellent structural and optical properties of ZnSe. The best material was grown on undoped GaAs at the VI/II ratio near unity. The full-width-at-half-maximum (FWHM) of ZnSe (∼0.2/μm thick) x-ray peak as low as 90 arc seconds was achieved. TEM results also show very low defect density. The density of stacking faults is less than 105/cm2 which is four orders of magnitude less than that of samples grown by conventional MBE [J. Petruzzello et al. J. Appl. Phys. 63, 2299 (1988)] and MOCVD [J.L. Batstone et al. Philos. Mag A, 66, 609, 1992]. The spacing between misfit dislocations is between 5 to 10,μm which is one order of magnitude larger than that of reported sample of comparable thickness.

We will report the photo-assisted heteroepitaxial growth of Znx Cdl-xS by Metalorganic Vapor Phase Epitaxy (MOVPE). Sources materials were diethylzinc, dimethylcadmium and tertiaributylmercarptan. We have studied the effect of light intensity on the change of the Zn composition, crystalline quality and optical properties of epitaxial layers grown on (100) GaAs substrates. The Zn composition of the films could be increased by ≃ 15% by illuminating layers during the growth at 400°C. Concerning the characterization of epilayers, we observed a bright luminescence peak at E = 2.80 eV for x≃ 0.4. Epilayers with the best crystalline quality we could grown exhibited a full width at half maximum of ≃ 70 arsec by x-ray diffraction rocking curves when grown at 380°C.

A novel zinc precursor adduct tetramethylmethylene diamine: dimethylzinc (TMMD:DMZn) has been used to grow ZnSe-ZnS strained layer superlattices by low pressure MOVPE at 300'C. The use of this new precursor leads to improved material purity and lower homogeneous gas phase premature reaction than in the case of dimethylzinc. Optical characterization has been made between liquid helium and room temperature. The 2K photoluminescence lines range between 2.85 eV and 3.15 eV. The 2K photoluminescence is characterized by a linewidth at half maximum ranging from 13-45 meV. Additional reflectivity and photoreflectance experiments have been carried out to measure light-hole excitons. A variational calculation of the Rydberg energies has been performed using a sophisticated trial function. The experimental data is in agreement with the theoretical value when a small conduction band offset is used.

We have used low pressure MOVPE to grow a series of short-period ZnSe-ZnTe strained-layer superlattices onto either ZnSe or ZnTe buffer layers. Typical superlattice periods range from 2 to 6.5 nm with constant ZnSe thickness of 2 monolayers. X-Ray diffraction analyses have shown that the superlattices are free-standing if grown on a ZnSe buffer but lattice matched to ZnTe if grown on ZnTe buffer layers. The luminescence emitted by the free standing samples has been studied using both the photoluminescence technique at low temperature and cathodoluminescence at higher temperature, for improved pumping. Our samples exhibit a complicated temperature dependence similar to the behaviour of ZnSeTe alloys where exciton self-trapping to tellurium gives strong photoluminescence bands labelled SI and S2. A high temperature, high energy feature is observed and is associated with the fundamental superlattice transition. The energy position of this structure suggest a high value of the ZnSe/ZnTe valence band offset, in the range 1200-1400 meV.

Photoluminescence (PL) experiments at 2K are performed on MOCVD grown MnSe. The precursors used in the growth stage are methylpentacarbonylmanganese and diethylselenide. Pyrolysis of the percursors is realized inside a gradient reactor under a constant H2 flux, between 280-55°TC. The compound is epitaxially grown on various substrates (Si, InP, GaSb, GaAs, ZnTe/GaAs, etc.). On some of these samples the compound presents a zinc blende structure, while in the other samples rock salt formation has been identified. The first substrate is used because of its interest in Si technology, while the others are used because MnSe can be grown in the zinc blende phase for very thin layers. For the first time x-ray diffraction data has allowed us to determine the lattice constant of zincblende MnSe (aMnse (oct)=5.818Å), confirming the close approximation (a ∼ 5.9Å) used from the Zn1-xMnxSe alloy. These compounds have visible Mn++ transitions at 2.12-5eV; other features are also visible at 2.3-4, 2.7, and 3.0eV. The energy gap transition of tetrahedral thin film layers of MnSe is seen for the first time in PL spectra. A temperature dependant PL study is performed on MnSe in the 2-200K range. Reflectivity experiments are used to attempt to identify the internal manganese transitions. A qualitative PL analysis of the samples grown at different temperatures and on different substrates is provided. A Stokes shift is encountered when the results are compared.

Although heteroepitaxy of lattice-matched and lattice-mismatched materials leading to artificially structured materials has resulted in impressive performance in various electronics devices, material combinations are usually limited by lattice matching constraints. A new concept for fabricating material systems using the atomically abrupt and low dimensional nature of layered materials, called van der Waals epitaxy (VDWE), has been developed. GaSe (Eg = 2.1 eV) has been deposited on the three dimensional surface of GaAs (111) using a molecular beam deposition system. GaSe was evaporated from a single Knudsen source, impinging on a heated substrate. Even with a lattice mismatch of 6% between the substrate and the growing film, good quality single crystal films were grown as determined by RHEED. The films have further been analyzed using a complementary combination of XPS and X-ray reflectivity.