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Notes: Optically transparent and electrically conductive cadmium tin oxide is employed in vertical cavity surface-emitting lasers for vertical current injection. Continuous wave lasing at room temperature is achieved in GaAs/AlGaAs quantum well lasers. Devices with a 10 μm optical window, which also serves as a vertical current injection inlet, give lasing threshold currents as low as 3.8 mA. The differential series resistance is 350–450 Ω with a diode voltage of 5.1–5.6 V at lasing threshold. Far-field pattern of the laser emission is Gaussian-like with a full width at half maximum of 7°.

Notes: Single GaAs/AlxGa1−xAs quantum wells, grown by molecular beam epitaxy with growth interruptions at each interface, are investigated using low-temperature photoluminescence. The three clearly resolved photoluminescence peaks are attributed to discrete monolayer thicknesses of the well. The splitting of the peaks is investigated for several hundred points across a 2 in. wafer. The negligible variation of the peak splitting is consistent with abrupt interfaces in the growth direction, atomically smooth interfaces, and discrete thicknesses of the quantum well with changes of only integer multiples of monolayers.

Notes: The effect of the ambient conditions in the growth chamber of the molecular beam epitaxy machine during the growth of GaAs/Al0.35Ga0.65As structures was investigated. Both growth-interrupted (120 s at each heterointerface) and uninterrupted surfaces and interfaces were evaluated using a growth temperature of 580 °C. Two ambient conditions were studied: (a) ∼1×10−10 Torr O2; and (b) ultrahigh vacuum (UHV, ∼5×10−11 Torr, with no intentional introduction of contaminants). A striking difference was observed in both the 1.7 K photoluminescence (PL) spectra of single quantum well (SQW) structures and UHV scanning tunneling microscopy (STM) of surfaces, which were grown under ambient condition (a) as opposed to (b). When consecutive growth-interrupted SQW samples were grown with different well widths (25 and 28 A(ring)) under condition (a), the emission energy splitting into several peaks was observed, indicating discrete thicknesses of the well. However, the peak energies shifted as the laser spot was scanned across each sample. Additionally, the peak energy shifted from sample to sample for the same nominal well width.On the other hand, when SQW samples were grown under condition (b), no variation in the emission energy was observed as the laser was scanned across the sample, or from sample to sample for a given well width. Furthermore, the PL observations are supported by UHV-STM results. UHV-STM images indicated a very rough surface with large islands containing small terraces on top (a bimodal distribution) for condition (a). Conversely, when samples were grown under condition (b), only large islands were observed. For growth interrupted GaAs surfaces, 400 A(ring)×600 A(ring) islands were observed, and for Al0.35Ga0.65As, they were 150 A(ring)×400 A(ring), with a one-monolayer step in between islands. These data are consistent with abrupt interfaces with only a single-mode distribution for growth-interrupted surfaces. On the other hand, UHV-STM images of uninterrupted GaAs surfaces grown under condition (b) showed islands that were 40–60 A(ring) across. Photoluminesce spectra of a similarly grown SQW sample showed only a single broad emission line, consistent with an interface configuration of many steps which are smaller than the exciton diameter. The results show that interface roughness is sensitive to background O2.

Notes: Electron transport in quantum well modulation δ doped on either the normal or the inverted side has revealed the major cause of the long-puzzling inferior transport characteristics of the inverted interface. For growth conditions optimized for best transport with normal-side doping, we find migration of the Si dopant toward the inverted interface during growth to be the primary reason for the reduced inverted well mobility. This new understanding has allowed us to grow modulation-doped inverted quantum wells of unprecedented quality having electron mobilities as high as 2.4×106 cm2/V s at 4.2 K and 3.0×106 cm2/V s at 1.0 K.

Notes: Spatial localization of Be in δ-doped GaAs within few lattice constants (〈20 A(ring)) is achieved at low growth temperatures for concentrations N2DBe 〈1014 cm−2 as indicated by capacitance-voltage profiles and secondary ion mass spectroscopy. At elevated growth temperatures and at higher Be concentrations, significant spreading of the dopants occurs and is explained by (i) Fermi-level pinning-induced segregation, (ii) repulsive Coulomb interaction of dopants, and (iii) diffusion. The highest Be concentration achieved at low growth temperatures exceeds 2×1020 cm−3 and is limited by repulsive dopant interaction. It is shown that the repulsive Coulomb interaction results in a correlated, nonrandom dopant distribution. The diffusion coefficient of Be in GaAs is determined and is found to be much lower than previously reported.

Notes: The spatial resolution of the capacitance-voltage profiling technique on semiconductors with one-dimensional quantum confinement is shown to be given by the spatial extent of the wave function. The Debye length limitation does not apply. Capacitance-voltage profiles on δ-doped GaAs of density 4–4.5×1012 cm−2 exhibit widths of 20 and 48 A(ring) for p- and n-type impurities, respectively. The profiles agree with the theoretical resolution function and with Be and Si profiles measured by secondary-ion mass spectroscopy. It is further shown that the saturation of the free-carrier density of highly Si δ-doped GaAs grown by molecular beam epitaxy is due to inactive Si impurities

Notes: Quarter-wave semiconductor mirrors of InP-In0.53Ga0.47As for high reflectivity at 1.65 μm wavelength are epitaxially grown using metalorganic chemical vapor deposition. Doping of the In0.53Ga0.47As layers is found to be critical for high reflectivity at wavelengths corresponding to the In0.53Ga0.47As band gap. n-type doping reduces the band-to-band absorption resulting in high reflectivity while p-type doped mirrors show reduced reflectivity.

Notes: In suitably designed resonant tunneling double barriers the capacitance-voltage curve exhibits well-defined features corresponding to the charging and discharging of the quantum well. From the bias dependence of the electron density in the well we find that in our thick parabolic wells, electrons tunneling into the excited states relax to the lowest subband and sequentially tunnel out. Our experiments allow us to obtain the charge density accumulated in the well and the tunneling escape rate of electrons out of the well.

Notes: Continuous-wave room-temperature operation is reported for the first time of vertical cavity current injection semiconductor lasers with a metallic reflector. The GaAs/(AlGa)As lasers have low-threshold currents of 8 mA for 8-μm-diam contacts and threshold current densities of 9.5 kA/cm2. Single longitudinal mode and bimodal operation are obtained for short and long Fabry–Perot étalons, respectively. The spectral width of the single-mode laser line is 0.1 A(ring). The laser structures have a very small series resistance which results in a voltage drop of 1.8 V along the diodes at lasing threshold.