Electrical Characterization of Different Passivation Treatments for Long-Wave Infrared InAs/GaSb Strained Layer Superlattice Photodiodes

Abstract

Silicon dioxide (SiO 2 ), silicon nitride (Si x N y ), and zinc sulfide (ZnS) with ammonium sulfide [(NH 4 ) 2 S] as a prepassivation surface treatment were compared as passivants for InAs/GaSb strained layer superlattice detectors with a 0% cutoff wavelength of $10 lm. SiO 2 did not show significant improvement and the zero-bias resistance-area product (R 0 A) was 0.72 X-cm 2 at 77 K. Si x N y passivation showed a nominal improvement with an R 0 A value of 4.1 X-cm 2 at 77 K. ZnS with (NH 4 ) 2 S treatment outperformed others significantly, improving the R 0 A value to 492 X-cm 2 at 77 K. Variable-area diode measurements indicated a bulk-limited R 0 A value of 722 X-cm 2 . ZnS-passivated diodes exhibited maximum surface resistivity with a value of 2500 X-cm.

Passivation of long-wave infrared InAs/GaSb strained layer superlattice detectors

“…We attribute this to the band bending at the semiconductor surface caused by the nature of band alignment at the passivant-semiconductor interface and the presence of fixed charges inside the passivation layer. The fixed charge density in electron-beam evaporated ZnS is expected to be lower than in SiN x deposited under a plasma environment [27]. In addition, ZnS facilitates saturation of surface states by formation of sulphur bonds by constituent atoms of InAs/GaSb SLS.…”

“…Photodetectors operating in the long-wave infrared (LWIR, [8][9][10][11][12][13][14] lm) spectral band could be potentially useful for a wide variety of applications such as meteorology, astrophysical imaging, missile detection and tracking, and satellite based surveillance. The technologies currently dominating those applications in this wavelength range are based on interband Mercury-CadmiumTelluride (MCT) and intersubband quantum well infrared (QWIP) detectors.…”

“…With shifting of detector operation wavelength into the LWIR region, passivation issues become even more important due to reduced bandgap of detectors. A number of studies have investigated the effect of several passivation techniques on LWIR SLS detector performance employing dielectric passivation (with silicon dioxide [6], polyimide [7] or photoresist [8,9]), chalcogenide passivation (with ammonium sulfide [10] and zinc sulfide [11]), and overgrowth with larger bandgap material [12]. An elegant approach to the solution of the surface leakage current problem is the recently proposed nBn detector design [13].…”

Effect of the oxide-semiconductor interface on the passivation of hybrid type-II superlattice long-wave infrared photodiodes

“…3 Many passivation studies have ignored the interface and focused on how to encapsulate the mesas using polymers 4-6 or inorganic dielectrics. [6][7][8] To meet both requirements, others have combined sulfur-based treatments with an encapsulant, 7,9 or used epitaxial overgrowth of a large bandgap material. 10 A further approach to suppressing surface currents is to reduce the exposure of narrow gap materials to the environment by using wider bandgap layers in the high field regions around the junction 11-13 or a "shallow etch" that isolates neighboring devices but terminates within a wider bandgap layer.…”

Study of Short- and Long-Term Effectiveness of Ammonium Sulfide as Surface Passivation for InAs/GaSb Superlattices Using X-Ray Photoelectron Spectroscopy

“…[10][11][12] However, to prevent degradation of device performance over time and to maintain good long-term stability of (NH 4 ) 2 S-passivated SLS detectors, and III-V devices in general, a thin layer of encapsulating material has been used. [13][14][15][16][17][18] Though it is natural to assume that a similar mechanism is responsible for the enhancement of electrical properties of InAs/GaSb SLS photodetectors treated with (NH 4 ) 2 S, a detailed surface study was never performed to confirm this. In this work, as-etched and (NH 4 ) 2 S-treated samples of an InAs/ GaSb SLS structure, which was designed to operate in the LWIR region, were studied using x-ray photoelectron spectroscopy (XPS) to verify the proposed passivation mechanism.…”