摘要:

Two series of high‐quality, unintentionally doped GaAs films were grown to evaluate a solid As cracker source with a graphite crucible. In the first series, material properties comparisons were made between a film grown with the As cracker in the dimer mode, a film from the same cracker source but in the tetramer mode, and lastly, a film from a conventional As cell. The film grown with the dimers had an‐type unintentional background doping level of 5×1014cm−3and a 104 000 cm2/V s mobility at 77 K. The films grown with As tetramers gave lowp‐type unintentional background doping levels of less than 1.1×1014cm−3, respectively. Photoluminescence spectra taken of these films at 4 K showed various excitonic transitions and comparableCincorporation. In the second series, films grown at As2/Ga incorporation rate ratios of 1.1, 1.5, and 2.0 had layers that werep‐type, resistive, andntype, respectively. Samples taken from the film grown at the 2.0 ratio had 77 K mobilities as high as 195 000 cm2/V s, with a corresponding net carrier concentration of 3.8×1014cm−3. These mobility values are the highest reported for GaAs grown with a solid As dimer source. Results from a variable temperature van der Pauw measurements of another sample cut from this film gave a donor ionization energy of 2.6 meV.

ISSN:1071-1023    

DOI:10.1116/1.584846

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

A novel effusion furnace for the production of As2from As4by combined thermal and catalytic cracking has been evaluated in a Varian GEN II molecular‐beam epitaxy (MBE) system. The furnace consists of two temperature zones with a one‐piece all‐tantalum combined crucible, delivery tube, and cracking zone. Ta baffles are inserted into the cracking zone. Thermal isolation of the ‘‘warm’’ sublimation zone and the ‘‘hot’’ cracking zone is achieved by water or liquid nitrogen cooling of the sublimation zone. With the cracking zone at 1500 °C and no power to the 200 cc capacity sublimator, the sublimation zone rises to only 75 °C. Cracking of As4begins at about 750 °C and saturates at about 900 °C. The As flux stabilizes in about 1.25 h. Installation of the cracker furnace in a position previously used for the old As effusion furnace resulted in considerable outgassing due to the previous condensation of As and trapped impurities on the cryoshroud around the mouth of the old furnace. Soon after installation, growth of nominally undoped GaAs in the As4mode (by holding the cracking zone at 400 °C) gave background doping concentrations ofp=2×1014/cm3, but the first attempts at growth of nominally undoped GaAs with As2gave highn‐type background doping levels due to the outgassing mentioned above. A combination of secondary ion mass spectroscopy (SIMS) and photoluminescence analysis showed decreased C and increased S in the As2grown layers. Following mechanical scraping and extended thermal cleaning of the shroud area around the cracking zone, the residual As2background doping dropped dramatically (to high 1013/cm3) while still remainingntype. Material and device benefits we have observed for As2grown GaAs and (Al,Ga)As are: slightly improved surface morphology, decreased C incorporation, increased doping efficiency in (Al,Ga)As:Si, greatly improved low‐temperature photoluminescence, and excellent heterojunction acoustic charge transport (HACT) device results.

ISSN:1071-1023    

DOI:10.1116/1.584847

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

The technique and some applications of a graded‐thickness sample deposition method for molecular‐beam epitaxy (MBE) are described. We discuss the use of this method for the growth of GaAs on Si and related materials systems. In this method the substrate is translated during growth relative to a fixed, near‐sample‐plane shutter so that a wedge shaped growth thickness profile is obtained. We have found this method to be especially useful in conjunction with bothexsituandinsituanalytical techniques for probing the continuous evolution of thin film growth. The technique offers several advantages over the traditional method of preparing a series of samples of different thicknesses. We have also found it useful for the direct comparison of the evolution of growth of two different surface preparations. We describe the use of Auger forinsitumeasurement of the composition and structure of the film at various stages of the growth with near monolayer resolution. Rutherford backscattering (RBS) has been used as anexsituprobe of the evolution of the deposited film. In an attempt to understand and control the atomic scale processes during the initiation of growth at the GaAs–Si interface we have used this method to grow graded‐thickness samples with total thickness 3.5–10 nm. Analysis of these films has led us to develop a model for the nucleation and initial stages of growth of GaAs‐on‐Si. We also report on possible device applications of this technique.

ISSN:1071-1023    

DOI:10.1116/1.584848

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

A new class of III–V based diluted magnetic semiconductors, specifically In1−xMnxAs (x≲0.2) and InAs/InMnAs multilayer structures, has been prepared by molecular beam epitaxy. The x‐ray diffraction measurements reveal that the incorporation of Mn can be predominantly either homogeneous (200 °C) or inhomogeneous (300 °C), depending on the growth temperature. Semiconducting properties of the films have been examined by optical absorption and Hall effect measurements, and it has been found the films of homogeneous alloy aren‐type and have a band gap which decreases with increasing Mn composition. Magnetization measurements indicate that the homogeneous alloy exhibits paramagnetic behavior, whereas ferromagnetic behavior dominates for the inhomogeneous case. The growth of GaMnAs has also been examined.

ISSN:1071-1023    

DOI:10.1116/1.584849

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

A double‐oven cracking furnace has been used to produce a flux composed of smaller selenium molecular species for the molecular‐beam epitaxy (MBE) growth of ZnSe on (100) GaAs substrates. Mass spectrometric analysis of fluxes from a conventional effusion cell and the cracking oven showed a significant difference in the number of large selenium molecules Sen(n>2) in their mass spectra. This new selenium source was found to be reactive with GaAs and its oxides, therefore its reaction with the substrate reduced the effectiveness in desorbing the oxide layer by heat treatment. Using the cracked selenium source, unintentionally doped ZnSe films have been grown on GaAs substrates desorbed in a separate ultrahigh vacuum (UHV) chamber linked to the MBE system. These undoped layers were highly resistive at room temperature and had low‐temperature photoluminescence spectra dominated by emission from the recombination of free excitons, comparable to the best layers grown using an uncracked selenium source.

ISSN:1071-1023    

DOI:10.1116/1.584850

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

We have been able to incorporate As into molecular‐beam epitaxy (MBE) grown ZnSe in the range of 1017–1021atoms/cm3using Zn3As2as the As source. This contrasts with very low As levels we obtained using an As cracker cell. The As incorporation is highly nonlinear with Zn3As2flux and depends on the excess Se used. Several samples doped with Zn3As2show low temperature photoluminescence with near band edge emission dominated by shallow acceptor levels. We will describe the details of several growth variations studied and their influence on As incorporation.

ISSN:1071-1023    

DOI:10.1116/1.584851

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

A newinsitutechnique has been developed to measure the growth surface temperature of a substrate, and to calibrate the temperature of substrate holders. The technique has been demonstrated to be accurate to better than 5 °C and was verified for calibrating substrate temperatures between 160–220 °C. Condensation of an incident Te2flux occurred on CdTe surfaces when the flux of the incident Te2dimers exceeded the flux desorbing from the surface. The surface temperature at the onset of condensation was calculated by equating the expressions for the incident Te2flux and the desorbing Te2flux. Experimentally, the onset of condensation was determined by a change in the reflection high‐energy electron diffraction pattern of the substrate.

ISSN:1071-1023    

DOI:10.1116/1.584807

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

The design and operation of a two‐zone furnace and crucible for the evaporation of II–VI semiconducting materials is described. The furnace contains separate heating elements and temperature sensors for each of the zones. The second zone is located at the open end of the furnace. The use of two independently‐controlled temperature zones allows for the elimination of clogging problems that often occur with the evaporation of materials such as tellurium. The pyrolytic boron nitride (PBN) crucible contains a cap with a 2 mm inside diameter and 16 mm long orifice, which is designed to yield higher operating temperatures and better flux stability. A special PBN crucible retainer has also been designed to minimize contact of evaporated material with the tantalum structure of the furnace.

ISSN:1071-1023    

DOI:10.1116/1.584808

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

The successful preparation of lattice matched buried heterostructure (BH)PbEuSeTe lasers grown by molecular‐beam epitaxy (MBE) is reported here for the first time. Lasers with 2–8 μm wide and 0.5 μm thick buried Pb1−xEuxSeyTe1−yactive layers, in the composition range of 0≤x≤0.015 and cavity lengths between 200 and 300 μm, were fabricated. Single mode operation was realized in most devices for injection currents 1.2 to 4.5 times the threshold current. A maximum continuous wave (cw) operation temperature of 180 and 176 K was measured for BH diode lasers with PbTe and PbEuSeTe (0.22 at. % Eu) active layer compositions, respectively. Using a high‐resolution scanning electron microscope, growth discontinuities were found in the nonplanar regions of the second cladding and capping layers. In most cases, lower threshold current densities were measured for BH lasers in comparison to double heterostructure (DH) lasers with the same active layer composition. It is believed that improvement of growth morphology, and optimizing layer thicknesses and doping profiles will lead to lower threshold currents and higher operation temperatures in BH lasers.

ISSN:1071-1023    

DOI:10.1116/1.584809

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

Photoassisted molecular‐beam epitaxy (MBE) has been employed to successfully preparep‐type andn‐type modulation HgCdTe. In this paper, we report details of the MBE growth experiments and describe the structural, optical, and electrical properties that these new quantum well structures and superlattices of HgCdTe possess.

ISSN:1071-1023    

DOI:10.1116/1.584810

出版商:American Vacuum Society    

年代:1990

数据来源: AIP