Optimization of GaN window layer for InGaN solar cells using polarization effect

The III-nitride material system offers substantial potential to develop high-efficiency solar cells. Theoretical modeling of InGaN solar cells indicate strong band bending at the top surface of p-InGaN junction caused due to piezoelectric polarization-induced charge at the strained p-GaN window interface. A counterintuitive strained n-GaN window layer is proposed, modeled and experimentally verified to improve performance of InGaN solar cells. InGaN solar cells with band gap of 2.9 eV are grown using MOCVD with p-type and n-type strained GaN window layers, and fabricated using variable metallization schemes. Fabricated solar cells using n-GaN window layers yield superior VOC and FF compared to those using p-GaN window layers. The VOC's of InGaN solar cells with n-GaN window layers are further enhanced from 1.5 V to 2 V by replacing the conventional NiOX top contact metal with Ti/Al, which also verifies the tunneling principle.

[1]  John B. Shoven,et al.  I , Edinburgh Medical and Surgical Journal.

[2]  G. G. Stokes.  "J." , 1890, The New Yale Book of Quotations.

[3]  G. Kamath,et al.  Large-area high-efficiency (AlGa)As—GaAs solar cells , 1977, IEEE Transactions on Electron Devices.

[4]  W. Ebeling.  Endoreversible Thermodynamics of Solar Energy Conversion , 1995 .

[5]  Shuji Nakamura,et al.  The Blue Laser Diode: GaN based Light Emitters and Lasers , 1997 .

[6]  R. Langer,et al.  Giant electric fields in unstrained GaN single quantum wells , 1999 .

[7]  Lester F. Eastman,et al.  Two-dimensional electron gases induced by spontaneous and piezoelectric polarization charges in N- and Ga-face AlGaN/GaN heterostructures , 1999 .

[8]  Fu-Rong Chen,et al.  Low-resistance ohmic contacts to p-type GaN achieved by the oxidation of Ni/Au films , 1999 .

[9]  Vincenzo Fiorentini,et al.  Spontaneous versus Piezoelectric Polarization in III–V Nitrides: Conceptual Aspects and Practical Consequences , 1999 .

[10]  Shuji Nakamura,et al.  The blue laser diode-the complete story , 2000 .

[11]  S. Jeon,et al.  Lateral current spreading in GaN-based light-emitting diodes utilizing tunnel contact junctions , 2001 .

[12]  Pierre Lefebvre,et al.  High internal electric field in a graded-width InGaN/GaN quantum well: Accurate determination by time-resolved photoluminescence spectroscopy , 2001 .

[13]  Vincenzo Fiorentini,et al.  Nonlinear macroscopic polarization in III-V nitride alloys , 2001 .

[14]  T. Wen,et al.  Low-operation voltage of InGaN-GaN light-emitting diodes with Si-doped In/sub 0.3/Ga/sub 0.7/N/GaN short-period superlattice tunneling contact layer , 2001, IEEE Electron Device Letters.

[15]  Hiroshi Harima,et al.  Absorption and Emission of Hexagonal InN. Evidence of Narrow Fundamental Band Gap. , 2002 .

[16]  Hiroshi Harima,et al.  Optical bandgap energy of wurtzite InN , 2002 .

[17]  Eugene E. Haller,et al.  Temperature dependence of the fundamental band gap of InN , 2003 .

[18]  Yoshiki Saito,et al.  RF-Molecular Beam Epitaxy Growth and Properties of InN and Related Alloys , 2003 .

[19]  I. Ferguson,et al.  Crystalline perfection of GaN and AlN epitaxial layers and the main features of structural transformation of crystalline defects , 2007 .

[20]  Ian T. Ferguson,et al.  Design and characterization of GaN∕InGaN solar cells , 2007 .

[21]  M. Mehta.  Modifying PC1D to model spontaneous & piezoelectric polarization in III-V nitride solar cells , 2008 .

[22]  Thomas Ihn,et al.  Two-dimensional electron gases in heterostructures , 2009 .