Effect of a surface channel on the performance of a P-type Point Contact HPGe detector

Abstract The observation of anomalous charge collection in a P-type Point Contact (PPC) High Purity Germanium (HPGe) detector is reported. By studying preamplifier charge signals from the detector, these anomalous events are shown to be consistent with charge carrier drift along the surface of the detector, prior to collection at the contact. It is believed that these events arise from the formation of a surface channel in the detector. By coupling analysis of these experimental signals with field calculations, an estimate of the radial drift velocity of holes at the surface has been made. This value is found to be around 40 times slower than the accepted value for saturated hole drift in the bulk, and is in good agreement with that calculated using a newly developed technique for modelling carrier transport.

[1]  C. Ur,et al.  Characterization of a broad energy germanium detector and application to neutrinoless double beta decay search in $^{76}$Ge , 2010, 1012.5200.

[2]  Modelling surface-scattering effects in the solution of the Boltzmann transport equation based on the spherical-harmonics expansion , 1998 .

[3]  V. Riot,et al.  A digital signal processing module for gamma-ray tracking detectors , 2008 .

[4]  W. Shockley.  Currents to Conductors Induced by a Moving Point Charge , 1938 .

[5]  F. Stern,et al.  Electronic properties of two-dimensional systems , 1982 .

[6]  E. Kane,et al.  Energy band structure in p-type germanium and silicon , 1956 .

[7]  E. Hull.  Temperature sensitivity of surface channel effects on high-purity germanium detectors , 1995 .

[8]  D. Colman,et al.  Mobility Anisotropy and Piezoresistance in Silicon p‐Type Inversion Layers , 1968 .

[9]  Lino Reggiani,et al.  Hole drift velocity in germanium , 1977 .

[10]  J. R. Schrieffer,et al.  Effective Carrier Mobility in Surface-Space Charge Layers , 1955 .

[11]  Large-mass ultralow noise germanium detectors: performance and applications in neutrino and astroparticle physics , 2007, nucl-ex/0701012.

[12]  J. Llacer.  Geometric Control of Surface Leakage Current and Noise in Lithium Drifted Silicon Radiation Detectors , 1966 .

[13]  Physical modeling of hole mobility in silicon inversion layers under uniaxial stress , 2007 .

[14]  Computational models of germanium point contact detectors , 2012 .

[15]  H. Utsunomiya,et al.  Surface channel effect on γ-ray response functions of coaxial germanium detectors , 2005 .

[16]  R. Dinger.  Dead Layers at the Surface of p-i-n Detectors - A Review , 1975, IEEE Transactions on Nuclear Science.

[17]  D. Radford,et al.  A pulse shape analysis technique for the MAJORANA experiment , 2011 .

[18]  J. Llacer.  Study of Surface Effects in Thick Lithium Drifted Silicon Radiation Detectors , 1964 .

[19]  P. Solomon,et al.  Six-band k⋅p calculation of the hole mobility in silicon inversion layers: Dependence on surface orientation, strain, and silicon thickness , 2003 .