| dc.description.abstract | Single-photon avalanche diode (SPAD) can be used in self-driving cars, medical electronics, optical fiber communications, and etc. In the past, singlephoton avalanche diodes using silicon as the material have fewer defects, but the material bandgap limit makes it impossible to detect the light wavelength above 1100 nm. III-V SPAD based on InGaAs can be used to detect short-wave infrared (SWIR) light. However, III-V SPAD suffers from high defect density during epitaxy, which will cause more serious dark count and afterpulsing. In recent years, the literature shows that the use of indium aluminum arsenide (InAlAs) as the multiplication layer has a higher probability of breakdown and can be expected to have a higher single photon detection efficiency (SPDE), therefore, this thesis focuses on the fabrication and characteristics of the InGaAs/InAlAs SPAD.
In this thesis, InGaAs and InAlAs are respectively used as the absorption layer and the multiplication layer in the SPAD structure. The choose of material and the structure design aim to detect SWIR light. The device structure includes the absorption layer, the grading layer, the charge layer, and the multiplication
layer. In order to reduce the tunneling-induced dark carriers, the multiplication layer thickness should be increased, but accompanying with the increase of the
thickness is the deteriorated afterpulsing effect and timing jitter. Therefore, in order to overcome the dilemma of dark count rate, afterpulsing, and timing jitter, we propose a novel design in the multiplication layer. That is, an additional charge layer is added to divide the multiplication layer into high electric field and subhigh electric field region, so that the thickness of the actual effective breakdown is restricted to the high electric field region, which improves the afterpulsing effect and timing jitter, and meanwhile suppresses the tunneling current.
The SPAD is fabricated into a mesa structure to define the active detection window. We use two kinds of sidewall passivation which are benzocyclobutene (BCB) and polyimide (PI) that have been demonstrated to effectively reduce leakage current by the literature. For both devices fabricated with different passivation, the breakdown and punch-through voltage at room temperature are both 49 volts and 23 volts, respectively. The temperature coefficient is 49 mV/K. PI-passivation devices are thoroughly studied with the subsequent single-photon characteristic measurements. In addition, we also calculate the two-dimensional electric filed distribution of mesa structures with etching depths by the use of TCAD Silvaco tools. The mesa structures with different etching depths have notable effect on the confinement of central electric field and the suppression of peripheral electric field. The breakdown and punch-through voltage of both devices with different etching depths are 49 V and 23 V, respectively. The central
electric field can be better confined and the peripheral electric field can be better suppressed for the mesa structure with the first mesa etched to the first
multiplication layer than for that etched to the absorption layer.
The SPAD device is operated by a passively gated mode circuit and the ambient temperature is adjusted for temperature-dependent measurements. In order to reduce the afterpulsing effect and the dark count rate, we set the pulse width to 1.5 ns for measurement. From the measurement results, we find that the electric field distribution has a remarkable effect on the single photon
characteristics of SPADs. The devices etched to the multiplication layer have better performance in dark count rate and single-photon detection efficiency. The
effect of etching profile on the timing jitter and afterpulsing effect is non-monotonic under different temperatures. | en_US |