Double Heterojunction Diode Research Articles

Exciton localization and ultralow onset ultraviolet emission in ZnO nanopencils-based heterojunction diodes.

n-GaN/i-ZnO/p-GaN double heterojunction diodes were constructed by vertically binding p-GaN wafer on the tip of ZnO nanopencil arrays grown on n-GaN/sapphire substrates. An increased quantum confinement in the tip of ZnO nanopencils has been verified by photoluminescence measurements combined with quantitative analyses. Under forward bias, a sharp ultraviolet emission at ~375 nm due to localized excitons recombination can be observed in ZnO. The electroluminescence mechanism of the studied diode is tentatively elucidated using a simplified quantum confinement model. Additionally, the improved performance of the studied diode featuring an ultralow emission onset, a good operation stability and an enhanced ultraviolet emission shows the potential of our approach. This work provides a new route for the design and development of ZnO-based excitonic optoelectronic devices.

Negative resistance of reverse-biased PbSnTe/PbTe double heterojunction diodes

Reverse-biased PbSnTe/PbTe double heterojunction diodes uniquely exhibit negative resistance. This property is assumed to originate from point defects in the deep levels of the diode crystal structure.

Internal cooling efficiency of a junction diode

The three thermal rate equations were built newly up at both ends and at the junction of a p–n diode, in order to derive analytically the temperature difference ΔT (between a junction and both ends) and the internal cooling efficiency η defined newly for a homojunction diode. The maxima ΔT and η of a diode were derived analytically as a function of Vj within the short-length approximation and calculated numerically as a function of Vj or Vbi, where Vj is a voltage across the junction and Vbi is a built-in voltage at the junction. As a result, ΔT increases abruptly with an increase of Vj below Vj=0.050 V or of Vbi below Vbi=0.10 V, while above their values, it increases slowly with an increase of Vj or Vbi to saturate a certain value. For example, ΔT was estimated as 14.6 K for Hg0.8Cd0.2Te diode with Vbi=0.36 V. η has a local maximum of 63% at Vj≈0.01 V or at Vbi≈0.03 V, while above their respective values, it decreases abruptly with an increase of Vj or Vbi and falls to 4.4% at Vbi=0.80 V which is equivalent to that of a diode emitting a laser for fiber optical communication. However, the greater enhancements in ΔT and η of a diode are required to apply the internal cooling system to a laser-emitting diode which needs the exact control of temperature. These results should be useful for the application of the internal cooling system to the double heterojunction diode used in the optical communication.

Ultraviolet light emissions in MgZnO/ZnO double heterojunction diodes by molecular beam epitaxy

ZnO double heterojunction structure was grown by molecular beam epitaxy. 100 nm MgZnO/ZnO/MgZnO well was inserted between Ga-doped ZnO and Sb-doped ZnO layers. X-ray diffraction spectrum confirmed the preferential growth along c-direction and secondary ion mass spectroscopy measurements showed a clear double heterojunction profile of this structure. Thin MgZnO layers made no difficulties for electrons and holes to get into active intrinsic ZnO layer. Dominant ultraviolet electroluminescence was observed at the injection currents from 40 to 80 mA at room temperature. The output power was 7.3 times as that from p-n homojunction diode at the same driving current due to a good confinement of electrons and holes in the intrinsic ZnO layer.

Line-shape study of water vapour by tunable diode laser spectrometer in the 822?832�nm wavelength region

A near-infrared tunable diode laser absorption spectrometer is set up to measure the air-induced broadening coefficients and the line-strength parameters of water-vapour overtone transitions within the (2,1,1)←(0,0,0) band in the 822–832 nm wavelength region. A Hitachi HL8311 E double hetero-junction structure diode laser is used as a probe. The diode laser controller is home-built and stable within ±10 μA and ±10 mK, respectively. The laser-head mount has a simple design and provides easy access whenever changing of the laser head is required. The diode laser emission wavelength is thermally tuned between 50 °C and 12 °C. Thermal tuning of the diode laser emission wavelength is used to reveal the mode structure of the diode laser and to probe the overtone-band transitions of water vapour within its operating wavelength range. Current tuning of the diode laser is used at a fixed laser temperature to study the transitions one at a time. A balanced detector is used to improve the S/N ratio of the spectrum. A phase sensitive detection technique is followed to obtain the first-derivative spectra of the overtone transitions. The first-derivative spectra have been recorded at different air pressures inside the sample cell while the water-vapour pressure is kept fixed. The first-derivative spectrum is numerically integrated to obtain the original line shape. The original line shape is fitted with a Voigt profile by using a nonlinear least-squares fit program to extract the air-broadening coefficient and the line-strength parameter. The data obtained in our work is compared with the results of the HITRAN database.

The Growth and Characterization of Silicon/Silicon Carbide Heteroepitaxial Films on Silicon Substrates by Rapid Thermal Chemical Vapor Deposition

SiC and Si heteroepitaxial films were sequentially deposited on Si substrates to form Si/SiC/Si multilayer structures using a refined rapid thermal chemical vapor deposition (RTCVD) technology. Refined RTCVD is a combination of a graded composition process with rapid thermal chemical vapor deposition. The optimum growth conditions and characteristics of the as-grown films in the Si/SiC/Si multilayers were studied by structrual (X-ray, TEM) and electrical (four-point probe , Hall measurement) methods. N-Si/n-SiC/p-Si double-heterojunction diodes (DHD) were fabricated to determine the suitability of the multilayer films for device applications. Analysis of the I–V characteristics of the diode indicates that fine control of the thickness of the graded layers without degrading the crystallinity of the films results in high-quality heteroepitaxial SiC and Si films which are suitable for multilayer device applications.

Structural and transport properties of InAs/AlSb superlattices

We report the demonstration of molecular beam epitaxy (MBE) grown InAs/AlSb superlattices with properties suitable for cladding layer materials in semiconductor diode lasers operating in the 2–5 μm spectral range. X-ray rocking curves of these superlattices reveal excellent structural quality and small lattice mismatch ( Δa/ a = 1.2 × 10 −3) with respect to a GaSb substrate. Hall measurements reveal that controllable n-type doping of InAs/AlSb superlattices can be achieved by selectively codepositing silicon during growth of InAs layers. p-Type doping is performed by codepositing beryllium during growth of AlSb layers. InAs/AlSb superlattice p-n junctions have been fabricated and tested, yielding classical p-n diode current-voltage behavior. A simple double heterojunction diode laser, incorporating InAs/AlSb superlattice cladding layers and a Ga x In 1− xAs y Sb 1− y active layer, is demonstrated. The emission wavelength of the laser is 2.42 μm (2.50 μm) at 95 K (180 K).

Nitrogen doping in ZnSe by photo-assisted metalorgani vapor phase epitaxy

Doping characteristics of nitrogen in ZnSe using photo-assisted vapor phase epitaxy were investigated. The source precursors and the doping source were diethylzinc, dimethylselenide, and tertiarybutylamine. Photoluminescence, electrical properties of Schottky diodes, and electroluminescence from homo and double heterojunction diodes consistently supported p-type behavior of the ZnSe:N layers. At the conditions investigated, higher doping was achieved at lower substrate temperature and irradiation intensity; e.g., 350°C and 45 mW/ cm2, respectively. As a guideline, net acceptor concentration was estimated as 2 x 1017 cm-3 for the ZnSe:N layer with nitrogen concentration of 5 x 1017 cm-3 revealed by secondary ion mass spectroscopy.

Heterojunction Stripe Geometry Lead Salt Diode Lasers Grown By Molecular Beam Epitaxy

Abstract. Lead-rare earth-chalcogenide diode lasers have been grown by molecular beam epitaxy. Emission wavelengths shorter than 5 to 6 Am have been obtained from lead-europium-selenide-telluride (Pb1 -xEuxSeyTe1-y) double heterojunction diode lasers grown lattice-matched to PbTe substrates. Mesa diodes with -25 um wide stripes have been fabricated that have a wide range of single longitudinal mode emission at up to -1 mW/facet output power. These diodes have operated at up to 147 K cw, which to our knowledge is the highest cw operating temperature ever achieved with lead-chalcogenide diode lasers. The wavelength coverage of the PbTe system has so far been extended to 4.06 um cw. Longer wavelength coverage is obtained from double heterojunction diode lasers with Ma1-ySnyTe active regions lattice-matched to (Pb1-ySny)1-xYbxTe confinement layers. I n preliminary studies of diodes with x = 0.034, y = 0.14, the cw emission wavelength varied from 10.7 µm (at 10 K) to 7.1 µm (at 128 K).

Quantum well diode lasers of lead-europium-selenide-telluride

The formation of a new semiconductor compound, lead-europium-selenide-telluride, was recently demonstrated using the molecular beam epitaxy (MBE) growth technique. This material may be grown lattice matched to PbTe substrates, and double heterojunction diode lasers were fabricated which covered the wavelength range 6.6 to 2.7 μm. Operation up to 147 K has been attained, which is the highest cw operating temperature ever observed in lead-chalcogenide semiconductors. Single quantum well diode lasers in a lead-chalcogenide materials system have now been fabricated for the first time. These devices were composed of PbTe quantum wells with Pb1−xEuxSeyTe1−y confinement layers. The quantum wells ranged in thickness from 300 to 2500 Å. Strong quantum effects are observed for the smaller well widths (Lz ≲1200 Å) because of the small carrier masses (me∼mh∼0.037m0). The shift in laser emission energy is in approximate agreement with that calculated from a finite square well potential if ΔEc∼ΔEv is assumed. The near equality of the electron and hole effective masses makes it difficult to accurately determine ΔEc and ΔEv. The threshold current is strongly reduced by quantum effects, apparently because of modifications of the density-of-states function. The laser emission from these devices has been characterized by near-field and far-field measurements. At high temperatures (T≳90 K), the emission of these mesa stripe lasers switches from gain guided to an index guided mode. Single-mode emission up to ∼1-mW power levels have been observed. These lasers have tuned from 6.45 μm (at 13 K) to 4.41 μm (at 174 K) under cw conditions, and to 4.01 μm (at 241 K) pulsed. It appears that the maximum operating temperature is limited by the quantum well barrier height, and a preliminary experiment with a higher barrier gave pulsed operation up to 260 K. These are the highest pulsed and cw operating temperatures ever reported for lead-chalcogenide diode lasers, and puts them within the operating range of thermoelectric coolers. The total cw tuning range of a single diode laser is as large as 740 cm−1, which is also much larger than previously observed. These properties greatly enhance the utility of these devices for spectroscopic and fiber-optic applications.

Diode lasers of lead-europium-selenide-telluride grown by molecular beam epitaxy

It is desirable to extend the wavelength coverage of PbSnTe diode lasers to shorter wavelengths (λ<5 μm) and higher operating temperatures. Currently, this range is covered by PbSxSe1−x diode lasers operating below 100 K. Double heterojunction diode lasers have now been fabricated using a new materials system, Pb1−xEuxSeyTe1−y. These structures were grown lattice matched to (100) oriented PbTe substrates by molecular beam epitaxy using PbTe, Eu, Te, PbSe, Tl2Te (p dopant), and Bi2Te3 (n dopant) source ovens. Mesa diodes were fabricated with 20-μm-wide stripes using anodic oxide insulation. Diodes have so far been fabricated with up to x=0.010, y=0.011, which operated cw from 4.93 μm (at 30 K) to 4.06 μm (at 136 K). Diodes with x=0.0015, y=0.0020 have operated up to 147 K cw. This is the highest cw operating temperature ever attained with lead-chalcogenide diode lasers. A wide range of single mode operation with ∼1 mW output power was observed for some of the better diodes. These diodes are useful for ultrahigh resolution spectroscopy, and may be useful in the future for low-loss, long-wavelength fiber optics communications.

A novel p+n n+ GaAs/Al0.30Ga0.70As/GaAs double heterojunction diode for high-temperature electronic applications

Mesa-isolated, p+nn+, GaAs/Al0.30Ga0.70 As/GaAs, double heterojunction diodes are reported which have excellent electrical characteristics over the full temperature range from 23 to 400 °C. These devices have diode law ideality factors of approximately 1.1 at any temperature for forward current densities greater than 10−3 A/cm2 and have reverse leakage current densities of 4×10−10 A/cm2 at 23 °C and 2×10−2 A/cm2 at 400 °C. AlxGa1−x As is used only in critical device regions to ensure that GaAs heterojunction contacts are made to the wider band-gap materials and to allow the chemically reactive AlxGa1−x As to be encapsulated by GaAs. These results demonstrate that the GaAs/AlxGa1−x As chemical system is a good materials candidate in which to base a technology for electronic components operated at high temperatures.

The effect of facet mirror reflectivity on the spectrum of single-mode CW constricted double-heterojunction diode lasers

In this paper we show that the spectral mode content of mode-stabilized constricted douhle-heterojunction lasers can be altered by changes in facet reflectivity. If the facet reflectivity is substantially reduced below the nominal value of 30 percent, then the lasers will exhibit multilongitudinal mode operation. Nearly planar-geometry lasers that show instabilities can be made to operate in a stable single mode by increasing the facet reflectivity to values above 50 percent.

Low-threshold high- T o constricted double heterojunction AlGaAs diode lasers

Constricted double heterojunction diode lasers of relatively low CW thresholds (28-40 mA) are obtained by growing structures that maximize the amount of current flow into the lasing spot. These values are obtained while still using standard 10 microns wide oxide-defined stripe contacts. Over the 20-70 C temperature interval, threshold current temperature coefficients as high as 320 C and a virtually constant external differential quantum efficiency, are found.

Analysis of grating-coupled emission in lead-tin telluride diode lasers

The use of the grating-coupled emission concept with lead-tin telluride double-heterojunction diode lasers is analyzed theoretically. The GCE configuration is shown to be attractive for producing small divergence-angle emission from fixed-wavelength lead-salt devices, but to be of more limited interest for use with tunable lasers because of the small critical angle characteristic of the PbTe-air interface and because of the variation of the angle of emission with wavelength. The device structure studied is one incorporating a reflecting contact in close proximity to the grating, a feature which leads to resonant enhancement or reduction of the emission, depending upon the wavelength and the device dimensions.

Limitations of the direct-indirect transition on In1−xGaxP1−zAsz heterojunctions

Because In1−xGaxP1−zAsz is the highest-energy direct-gap alloy employed in laser diodes, we attempt to establish where the direct-indirect transition (xc+0.516yc=1.235, 77 °K) hinders or possibly even limits the use of this sytem in large-barrier (ΔE∼250 meV) double-heterojunction (DH) structures. The behavior at 300 and 77 °K of the I-V characteristics of single-heterojunction and homojunction structures employing high Ga composition (x?0.72, z≲0.01) wide-gap In1−xGaxP1−zAsz layers, lattice matched on GaAs1−yPy substrates, show that the nature of the direct-indirect transition of the ternary boundary In1−xGaxP (x∼xc, y=1 or z=0) acts as a limiting factor on the DH diode and laser performance of the quaternary system. As in GaAs1−yPy, donor states associated with subsidiary minima (X) cause a premature onset of the direct-indirect transition, and limit the growth of lattice-matched large-barrier In1−xGaxP1−zAsz (ΔE∼250 meV) DH lasers, with all layers direct, to substrates of composition y≲0.40.

The GaAs P-N-P-N laser diode

The general structure of double-heterojunction diode lasers is shown to be consistent with the required geometry of the Shockley diode or p-n-p-n switch. When the two devices are combined in a single structure, there results an extremely simple source of high optical power (>0.5-W) pulses of very short duration (<10 ns) without the need for a complex external driver. In principle, pulse triggering and repetition rate are easily controlled, suggesting that the device has potential application in pulse-coded optical communication systems.

Radiation trapping in laser diodes

This paper is concerned with the problem of cavity geometries which exhibit anomalously low radiative efficiencies. While the ideas presented apply to any type of cavity, the experiments and discussion refer specifically to the type of cavity of importance in commercial injection lasers, a Fabry-Perot cavity with cleaved end facets and sawed sidewalls. In this study, it is shown that the lowering of the external efficiency is probably associated with the excitation of internally circulating modes, analogous to those found in lasers with four cleaved sides. A dual-cavity diode structure is employed to demonstrate that it is the sidewall loss which controls the excitation of the internally circulating modes. To determine the geometric conditions for internal mode excitation in single and double heterojunction diodes, an extensive study was made of the combination of length, width, and facet reflectivity which lead to efficiency decreases. It is assumed that the internal modes are excited when the distributed sidewall loss for the internal modes is less than the distributed Fabry-Perot end loss for the externally radiated modes. The conditions for internal mode excitation and accompanying efficiency decrease are predicted by either assigning an empirically determined attenuation factor to the sawed side or assuming that the loss is associated with diffraction from small mirror segments at the sidewall which have been formed during the sawing operation. These predictions may be used to design Fabry-Perot sawed sidewall injection lasers so as to avoid efficiency loss through the excitation of internal modes.

Vacuum metallurgical equipment and processes: T Thorley,Metal Treatment Drop Forging, 33, 1966, 123–141

Reverse-biased PbSnTe/PbTe double heterojunction diodes uniquely exhibit negative resistance. This property is assumed to originate from point defects in the deep levels of the diode crystal structure.