摘要:

Transport of electrons tunnel injected into a superlattice (SL) is studied. The SL is placed in the base of ann‐p‐nbipolar transistor. By varying the emitter‐base forward bias (VEB), the energy of electrons injected into the base is varied. From the emitter and collector current measurements in the common‐base configuration, it is found that the electron transmission to the collector is strongly dependent on the injection energy, the currents showing a sharp peak, and the associated negative transconductance. The measurements show excellent agreement with the calculated values ofVEBat the onset of miniband conduction and at the suppression of injection into the SL due to enhanced quantum reflection by the SL minigap. The transfer characteristics also reveal a low‐current gain regime of electron transport below the onset of miniband conduction, implying conduction mediated by subminiband gap states.

ISSN:0003-6951    

DOI:10.1063/1.102822

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Temperature‐dependent photoluminescence (PL) measurements have been used to characterize 5‐&mgr;m‐thick Si(100) epitaxial layers dopedinsituduring molecular beam epitaxial growth with low‐energy (100, 500, and 1000 eV)11B+ions at growth temperatures of 500, 650, and 800 °C. Moderate doping (NB∼1017cm−3) yielded PL features comprised of both sharp and broad peaks in the boron bound exciton (B‐BE) region. At 4.2 K a broad B‐BE feature near 1086 meV dominated, although the sharp transverse optical phonon‐assisted B‐BE peak (B1TO) at 1092.5 meV was resolvable forNB<1017cm−3. Increasing the PL sample temperature above 4.2 K caused a rapid decay of the broad B‐BE peak intensity, thus permitting comparison of B1TOintensity for a range of ion energies and growth temperatures. At 10 K, a bulk‐like spectrum containing a sharp B1TOpeak with weaker multiexciton peaks B2TOand B3TOwas observed for the film growth at the highest temperature and lowest ion energy (800 °C and 100 eV). However, the intensity of the B1TOpeak decreased with decreasing growth temperature (constant ion energy) and with increasing ion energy (constant growth temperature). Samples grown at the lowest temperature (500 °C) displayed very different PL spectra with much weaker line emission, a rising PL background, and additional lines near 1040 meV due to ion‐induced residual lattice defects. Quenching of B1TOand the other sharp B‐BE peaks was accompanied by an increase in theN1 peak at 745.7 meV.

ISSN:0003-6951    

DOI:10.1063/1.102804

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Carrier decays following pulsed excitation in GaAs‐AlGaAs quantum wells have in the past been attributed to an excitonic recombination path. We show here that such an interpretation is inconsistent with the experimental evidence, and that the decays are controlled by recombination through electronic states at the GaAs‐AlGaAs interfaces. We discuss the expected magnitude of the decay times and the influence of carrier trapping on the decay process.

ISSN:0003-6951    

DOI:10.1063/1.102805

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Nominally undopedn‐type single crystals of ZnGeP2have been fabricated for the first time by high‐pressure vapor transport. These crystals have higher phosphorus concentration than melt‐grown bulk single crystals and exhibit lower sub‐band‐gap absorption in the transparency range between 0.64 and 12 &mgr;m. A heretofore unreported absorption peak at 13 &mgr;m and a transparency window extending from l5 &mgr;m to at least 23 &mgr;m have been identified in the infrared for these crystals, as well as in crystals grown from melt.

ISSN:0003-6951    

DOI:10.1063/1.103285

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Pseudomorphic high electron mobility heterostructures are demonstrated by atmospheric pressure metalorganic chemical vapor deposition for the first time. Transmission electron microscopy (TEM), variable temperature Hall effect measurements, Shubnikov–de Haas measurements, and photoreflectance were applied to characterize the heterostructures. TEM micrographs of the cross section reveal sharp heterojunction interfaces. Variable temperature Hall effect measurements show a monotonic increase in mobility as the temperature is lowered. With a spacer thickness of 120 A˚, a peak mobility of 80 000 cm2/V s at 20 K and a sheet carrier concentration of 1.05×1012cm−2are obtained. Similarly, a thinner spacer (60 A˚) shows a peak mobility of 57 000 cm2/V s at 25 K with a sheet carrier concentration of 1.40×1012cm−2. Shubnikov–de Haas measurements in magnetic fields up to 18.5 T show clear oscillations and the quantum Hall effect confirming the existence of a two‐dimensional electron gas.

ISSN:0003-6951    

DOI:10.1063/1.102806

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We calculate the change in the density of states due to a biased resonant tunneling structure. The maximum of the density of states near resonance gets shifted towards the low‐energy side compared to the unbiased case, as does the transmission coefficient, although the two need not be identical. For the case of asymmetric barrier heights, the left‐right symmetry of the density of states is broken when the field is nonvanishing.

ISSN:0003-6951    

DOI:10.1063/1.102807

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Nonplanar silicon oxidation in a dry O2+NF3gas mixture has been investigated. Oxide morphologies at silicon corners following 800 °C oxidation in dry O2and in dry O2+NF3gas are observed using a scanning electron microscope. While a serious decrease in oxide thickness at convex silicon corners is observed following oxidation in dry O2, no inhibition of oxide growth occurs and the Si/SiO2interface is smoothly rounded off at the corners following oxidation in dry O2+NF3. The effects of adding NF3gas to a dry O2atmosphere on nonplanar oxidation are discussed. Furthermore, a sacrificial oxidation in dry O2+NF3prior to forming the thin capacitor oxide is found to be very effective for reducing the oxide leakage current for a trenched capacitor.

ISSN:0003-6951    

DOI:10.1063/1.102808

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We present absorption measurements in HgCdTe/CdTe multiple quantum wells as a function of temperature, polarization, and well size in the 3–4 &mgr;m wavelength region. The energy levels are calculated using a model that includes band nonparabolicity. The spectra are fitted to a sum of continuous broadened steps including the two‐dimensional Sommerfeld enhancement factor. Polarization measurements confirm the assignment of heavy and light holes. The ratio between heavy and light hole absorption of 2.3/1 agrees well with theory. The fit of the linewidth with temperature shows a homogeneous linewidth of 4.6 meV times the density of longitudinal optical phonons and an inhomogeneous linewidth of 6.4 meV, which is similar to the alloy broadening in the bulk material.

ISSN:0003-6951    

DOI:10.1063/1.102809

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Raman area maps measuring the strain in lattice‐mismatched [111] and [001] oriented InxGa1−xAs/GaAs superlattices (x=0.1, 0.17) are presented and compared with independent x‐ray rocking curve studies of the average strain in the same samples. We find that the LO phonon frequency, but not the TO frequency, is a valid measure of strain for [111] oriented superlattices exhibiting one‐mode behavior. This is explained by the lack of compensation between the effects of alloying and strain for the TO mode in InxGa1−xAs. The capability to nondestructively map small growth variations in superlattice and buffer layer constituents is demonstrated.

ISSN:0003-6951    

DOI:10.1063/1.102810

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

InGaP/GaAs single quantum well(SQW) structure growth on GaAs facet wall is achieved by atomic layer epitaxy (ALE) using chloride source gases, such as InCl and GaCl. GaAs facets are formed on GaAs(100) surface openings by conventional hydride vapor phase epitaxy, which have {011} sidewalls perpendicular to the surface, {111}Band (100) faces. ALE growth of SQWs onto these faces results in a very smooth and uniform surface, as shown by scanning electron microscopy observation and cathodoluminescence measurements. The self‐limiting mechanism for ALE is also retained in such selective sidewall growth of heterostructures.

ISSN:0003-6951    

DOI:10.1063/1.102811

出版商:AIP    

年代:1990

数据来源: AIP