B.-C. Chung

Palo Alto Research Center, Palo Alto, California, United States

Are you B.-C. Chung?

Claim your profile

Publications (19)18.79 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The average device yield for high efficiency Al<sub>0.37</sub>Ga <sub>0.63</sub>As and GaAs n-p diode solar cells was increased, from below 25% to above 75%, by doubling the thickness of the GaAs cap layer to 0.6 μm. Low yields were characterized by a nonlinear shunting mechanism, which partially shorted the junction of the solar cell, independent of the various contact metals and thermal treatments used for ohmic contact formation
    IEEE Transactions on Electron Devices 02/1996; · 2.06 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Not Available
    Metalorganic Vapor Phase Epitaxy, 1992. Sixth International Conference; 07/1992
  • [Show abstract] [Hide abstract]
    ABSTRACT: A 25.2% efficiency measured under 1 sun, air mass 0 illumination has been achieved in a two‐terminal AlGaAs/GaAs/InGaAsP three‐junction solar cell. The cascade cell consists of a monolithic AlGaAs (E g =1.93 eV)/GaAs two‐junction mechanically stacked on an InGaAsP (E g =0.95 eV) single‐junction cell. The component cell of the AlGaAs/GaAs two‐junction structure were electrically connected using a metal interconnect fabricated during post‐growth processing. To minimize the obscuration effect introduced by the grid lines and metal interconnect, a prismatic cover glass was bonded to the AlGaAs/GaAs cascade cell. The results obtained with this structure represent the highest 1‐sun, air mass 0 efficiency achieved in any solar cell operating under a two‐terminal configuration. The implications of achieving this high efficiency in a two‐terminal, three‐junction solar cell for terrestrial and space applications are described as well.
    Applied Physics Letters 05/1992; · 3.79 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A 25.2% efficiency measured under 1-Sun, air mass 0 illumination has been achieved in a two-terminal AlGaAs/GaAs/InGaAsP three-junction solar cell. The cascade cell consists of a monolithic AlGaAs ( E <sub>g</sub>=1.93 eV)/GaAs two-junction mechanically stacked on an InGaAsP ( E <sub>g</sub>=0.95 eV) single-junction cell. The component cell of the AlGaAs/GaAs two-junction structure were electrically connected using a metal interconnect fabricated during post-growth processing. To minimize the obscuration effect introduced by the grid lines and metal interconnect, a prismatic cover glass was bonded to the AlGaAs/GaAs cascade cell. The results obtained with this structure represent the highest 1-Sun, air mass 0 efficiency achieved to date in any solar cell operating under a two-terminal configuration
    Photovoltaic Specialists Conference, 1991., Conference Record of the Twenty Second IEEE; 11/1991
  • B.-C. Chung, R.T. Green, H.F. MacMillan
    [Show abstract] [Hide abstract]
    ABSTRACT: Atomic layer epitaxy (ALE) techniques are utilized in a conventional atmospheric pressure OMVPE reactor to achieve heavily carbon-doped AlxGa1−xAs (O ≤x ≤ 1) layers. Trimethylgallium, trimethylaluminum and arsine are the chemical precursors used i the reaction. Organometallic species present in the reaction environment are the sources of carbon. It is observed that both the carbon and hole concentrations in the grown layers are higher in nonsaturated ALE growth (growth rate 1 atomic layer per cycle) as compared to that of the layers prepared in saturated ALE growth (growth rate = 1 atomic layer per cycle). Also, the presence of trimethylaluminum during growths has enhanced the incorporation of electrically-active carbon. Hole carrier concentrations as high as 2 × 1020 cm-3 have been achieved in Al0.5Ga0.5As layers. This is the highest electrically-active carbon doping level ever obta in growth by OMVPE. Device applications of this high carbon doping level to tunnel junction diode and nonalloyed contacts are demonstrated.
    Journal of Crystal Growth 01/1991; 107(s 1–4):89–95. · 1.55 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Component efficiencies of 0.2/sq cm cells at approximately 100x AMO light concentration and 80 C temperatures are not at 15.3 percent for a 1.9 eV AlGaAs top cell, 9.9 percent for a 1.4 eV GaAs middle cell under a 1.9 eV AlGaAs filter, and 2.4 percent for a bottom 1.0 eV InGaAs cell under a GaAs substrate. The goal is to continue improvement in these performance levels and to sequentially grow these devices on a single substrate to give 30 percent efficient, monolithic, two-terminal, three-junction space concentrator cells. The broad objective is a 30 percent efficient monolithic two-terminal cell that can operate under 25 to 100x AMO light concentrations and at 75 to 100 C cell temperatures. Detailed modeling predicts that this requires three junctions. Two options are being pursued, and both use a 1.9 eV AlGaAs top junction and a 1.4 eV GaAs middle junction grown by a 1 atm OMVPE on a lattice matched substrate. Option 1 uses a low-doped GaAs substrate with a lattice mismatched 1.0 eV InGaAs cell formed on the back of the substrate. Option 2 uses a Ge substrate to which the AlGaAs and GaAs top junctions are lattice matched, with a bottom 0.7 eV Ge junction formed near the substrate interface with the GaAs growth. The projected efficiency contributions are near 16, 11, and 3 percent, respectively, from the top, middle, and bottom junctions.
    Space Photovoltaic Research and Technology, 1989. 12/1990; -1:73-76.
  • [Show abstract] [Hide abstract]
    ABSTRACT: To evaluate the effects of the space environment on advanced III-V semiconductor solar cells, 19 experiments were placed on the LIPS III satellite. These experiments consisted of both single-junction GaAs cells and InGaAs and AlGaAs components for monolithic multijunction cells. The LIPS III satellite has been sending data to earth for nearly three years, and although the data have a large amount of scatter, there are enough data to start to make statistically meaningful observations on the relative performance of the cells on the panel. The cells, which, are protected by 20 mm coverslides, have displayed very little loss in short-circuit current. The short-circuit current is the performance parameter which can be most accurately derived from the available data. The III-V cells showed very little decay in short-circuit current after nearly three years in space
    Photovoltaic Specialists Conference, 1990., Conference Record of the Twenty First IEEE; 06/1990
  • B.-C. Chung, G.F. Virshup, J.C. Schultz
    [Show abstract] [Hide abstract]
    ABSTRACT: A 27.6% efficiency measured under 1-sun, air mass 1.5-global illumination has been achieved in a two-terminal monolithic two-junction cascade solar cell consisting of an Al<sub>0.37</sub>Ga<sub>0.63</sub>As ( E <sub>g</sub>=1.93 eV) upper cell and a GaAs lower cell. This result represents the highest 1-sun efficiency to date. The component cells were electrically connected using a metal interconnect contact fabricated during postgrowth processing. A prismatic cover glass was bonded to the cascade cell to minimize the obscuration effect introduced by the grid lines and metal interconnect contacts. As the cascade cell was operated under air mass 0 illumination, an efficiency of 23% was obtained. A 24.9% efficiency under 1-sun, air mass 0 condition has been achieved in a monolithic two-junction Al<sub>0.37</sub>Ga<sub>0.63</sub>As/Ga solar cell mechanically stacked on an InGaAs ( E <sub>g</sub>=1.0 eV) solar cell. This is the first demonstration of the high-efficiency GaAs-based three-junction solar cell. The implications of these high efficiencies, in either two-junction or three-junction cascade solar cells for terrestrial and space applications, are discussed
    Photovoltaic Specialists Conference, 1990., Conference Record of the Twenty First IEEE; 06/1990
  • [Show abstract] [Hide abstract]
    ABSTRACT: The component cell milestone goals for an AM0 30% efficient, three-junction, two-terminal cell operating at 70 to 100°C at 100X concentration are 16% top cell, 11% middle cell, and 3% bottom cell. The best values measured so far at 80°C and 100X are 15.27% for a 1.9 eV AlGaAs top cell, 9.87% for a 1.4-eV GaAs middle cell, and 2.40% for a 1.0 eV InGaAs bottom cell. At 25°C, these values increased to 15.42%, 10.79%, and 3.02%, respectively. The measured negative temperature coefficient for efficiency increases with decreasing bandgap so that higher bandgaps are preferred (such as a 1.0 eV bottom junction compared to a 0.7 eV one, other things being equal)
    Photovoltaic Specialists Conference, 1990., Conference Record of the Twenty First IEEE; 06/1990
  • [Show abstract] [Hide abstract]
    ABSTRACT: Temperature coefficients measured in solar simulators with those measured under AM0 solar illumination are compared to illustrate the challenges in making these measurements. It is shown that simulator measurements of the short-circuit current (delta Jsc/delta T) are inaccurate due to the mismatch between the solar spectrum and the simulators at the bandgaps of the solar cells. Especially susceptible to error is the delta Jsc/delta T of cells which are components in monolithic multijunction solar cells, such as GaAs filtered by 1.93-eV AlGaAs, which has an AM0 coefficient of 6.82 micro-A/sq cm/deg C, compared to a Xenon simulator coefficient of 22.2 micro-A/sq cm/deg C.
    02/1990;
  • [Show abstract] [Hide abstract]
    ABSTRACT: A 27.6 percent efficiency measured under 1-sun, air mass 1.5-global illumination has been achieved in a two-terminal monolithic two-junction cascade solar cell consisting of an Al0.37Ga0.63As (Eg = 1.93 eV) upper cell and a GaAs lower cell. This result represents the highest 1-sun efficiency to date. The component cells were electrically connected using a metal interconnect contact fabricated during postgrowth processing. A prismatic cover glass was bonded to the cascade cell to minimize the obscuration effect introduced by the grid lines and metal interconnect contacts. As the cascade cell was operated under air mass 0 illumination, an efficiency of 23 percent was obtained. A 24.9 percent efficiency under 1-sun, air mass 0 condition has been achieved in a monolithic two-junction Al0.37Ga0.63As/GaAs solar cell mechanically stacked on an InGaAs (Eg = 1.0 eV) solar cell. This is the first demonstration of the high-efficiency GaAs-based three-junction solar cell. The implications of these high efficiencies, in either two-junction or three-junction cascade solar cells for terrestrial and space applications, are discussed.
    01/1990;
  • [Show abstract] [Hide abstract]
    ABSTRACT: A 27.6% efficiency measured under 1 sun, air mass 1.5 illumination has been achieved in a two‐terminal, monolithic two‐junction cascade solar cell consisting of an Al 0.37 Ga 0.63 As (E g =1.93 eV) upper cell and a GaAs lower cell. The component cells were electrically connected together using a metal‐interconnect contact fabricated during post‐growth processing. Also, a prismatic cover glass was bonded to the front surface of the cascade structure to minimize the obscuration effect introduced by the grid lines and metal‐interconnect contacts. As the cascade cell was operated under air mass 0 illumination, an efficiency of 23.0% was obtained. Both results represent the highest 1 sun efficiencies ever reported. The implications of achieving this high efficiency in a two‐junction cascade solar cell for terrestrial and space applications are also described.
    Applied Physics Letters 11/1989; · 3.79 Impact Factor
  • B‐C. Chung, G. F. Virshup, J. G. Werthen
    [Show abstract] [Hide abstract]
    ABSTRACT: A high‐efficiency monolithic two‐junction solar cell consisting of an Al 0.37 Ga 0.63 As (E g =1.93 eV) upper cell and a GaAs lower cell has been grown by metalorganic vapor phase epitaxy. Since both component cells have the n‐on‐p configuration, the unwanted p‐n junction has been eliminated with the use of metal‐interconnect contact during post‐growth processing. As a two‐terminal device, an efficiency of 22.3% has been achieved under 1 sun, air mass 0 illumination conditions, whereas an efficiency of 23.9% was obtained when the cascade cell was operated as a three‐terminal device under 1 sun, air mass 1.5 illumination. This result represents the highest 1 sun efficiency ever reported. The advantages of utilizing this multijunction solar cell for terrestrial and space applications are also described.
    Applied Physics Letters 06/1988; · 3.79 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: 1.93 eV AlxGa1−xAs (x=0.37) n‐p solar cells with areas of 4 cm2 have been fabricated by metalorganic vapor phase epitaxy. Under 1 sun, air mass 1.5, simulated conditions, the cell exhibiting a conversion efficiency as high as 15% is characterized by a short‐circuit current density of 12.0 mA/cm2, an open‐circuit voltage of 1.42 V, and a fill factor of 0.87. The realization of these high‐quality AlGaAs solar cells at a band gap of 1.93 eV implies the potential for other promising optoelectronic devices in the visible spectrum.
    Applied Physics Letters 02/1988; 52(8). · 3.79 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: High-efficiency AlGaAs n-on-p solar cells with bandgaps at 1.75 and 1.93 eV have been achieved in the MOVPE (metal-organic vapor-phase epitaxy) growth structure. Power conversion efficiencies of 17.2% and 15.2% have been obtained in the 1.75 and 1.93 eV AlGaAs cells, respectively. A comparison of experimental values of short-circuit current as a function of bandgap to that of theoretical limits indicates that high-quality AlGaAs materials have been grown by MOVPE. The high efficiency obtained in the high-bandgap 1.93 eV AlGaAs cell implies the feasibility of high efficiency in lattice-matched AlGaAs(1.93 eV)/GaAs(1.42 eV) cascade cells.
    Photovoltaic Specialists Conference, 1988., Conference Record of the Twentieth IEEE; 02/1988
  • G.F. Virshup, B.-C. Chung, J.G. Werthen
    [Show abstract] [Hide abstract]
    ABSTRACT: A monolithically grown two-junction solar cell has been fabricated which produces 23.9% efficiency under AM1.5 global conditions and 22.3% under AM0 conditions. These are the highest one-sun efficiencies reported to date for both AM0 and AM1.5. The Al<sub>.35</sub>Ga<sub>.65</sub>As (1.93 eV) top cell and the GaAs (1.42 eV) bottom cell were grown by metal-organic chemical vapor deposition on GaAs substrates. Cell design and processing are described, and results of cell testing are presented.
    Photovoltaic Specialists Conference, 1988., Conference Record of the Twentieth IEEE; 02/1988
  • [Show abstract] [Hide abstract]
    ABSTRACT: Power conversion efficiencies as high as 16.5% under 1 Sun, air mass 1.5 (AM 1.5) illumination have been obtained for three-terminal, two-junction 1.72 eV AlGaAs/1.15 eV GaInAs monolithic cascade solar cells. The structures were grown by metal-organic chemical vapor deposition. The increased efficiencies arise primarily from improved surface morphology in this lattice-mismatched materials system. For the individual subcells in a cascade configuration, 1 Sun, Am 1.5 efficiencies as high as 10.4% and 15.3% are obtained for 1.15 eV GaInAs and 1.72 eV AlGaAs, projecting an eventual efficiency of 25.7% for the corresponding two-junction stack. Under 400 Sun concentration, these values are projected to increase to 12%, 19% and 31% respectively.In the lattice-matched 1.72 eV AlGaAs/1.42 eV GaAs materials system, the surface morphology has proved easier to optimize. Two-junction, two-terminal cascades in which the subcells are electrically connected by high-conductance junctions have been fabricated. Open-circuit voltages Voc as high as 2.01 V and fill factors as high as 0.86 have been obtained. These fill factors, comparable with those observed for the best single-junction cells under 1 Sun, AM 1.5 conditions, demonstrate the low residual resistance of the high-conductance junction.
    Solar Cells. 01/1988; 24:171-183.
  • [Show abstract] [Hide abstract]
    ABSTRACT: A monolithically grown two-junction solar cell has been fabricated which produces 23.9 percent efficiency under AM1.5 global conditions and 22.3 percent under AM0 conditions. These are the highest one-sun efficiencies reported to date for both AM0 and AM1.5. The Al(.35)Ga(.65)As (1.93-eV) top cell and the GaAs (1.42-eV) bottom cell were grown by metal-organic chemical vapor deposition on GaAs substrates. Cell design and processing are described, and results of cell testing are presented.
    01/1988;
  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper reviews recent progress at Varian to improve the efficiency of multijunction solar cells fabricated with GaAs-related materials. The most noteworthy achievement is the fabrication of a monolithic, two-terminal, two-junction AlGaAs/GaAs cell with a power conversion efficiency of 27.6% at 1 Sun, AM1.5 global. Recent results are presented for a number of single-junction and multijunction monolithic cell structures fabricated with the AlGaAs/GaAs/InGaAs materials system grown by metal-organic chemical vapor deposition. The progress and problems for lattice-matched and lattice-mismatched structures and cell interconnects are discussed and assessed. The latest results are significant steps toward demonstration of the viability of two- and three-junction cascade cells. The hurdles to be overcome in achieving efficiencies above 30% for 1 Sun and concentrator cells are discussed.
    Solar Cells.