改變電荷層摻雜濃度之砷化銦鎵/砷化銦鋁單光子累增二極體的特性探討;Characteristics of InGaAs/InAIAs Single Photon Avalanche Diodes with Changing Charge Layer Doping Concentration

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Title:	改變電荷層摻雜濃度之砷化銦鎵/砷化銦鋁單光子累增二極體的特性探討;Characteristics of InGaAs/InAIAs Single Photon Avalanche Diodes with Changing Charge Layer Doping Concentration
Authors:	林太皇;Lin, Tai-Huang
Contributors:	電機工程學系
Keywords:	電荷層摻雜;單光子累增二極體;電容;Charge layer doping;Single photon avalanche diodes;Capacitance
Date:	2020-01-21
Issue Date:	2020-06-05 17:40:14 (UTC+8)
Publisher:	國立中央大學
Abstract:	單光子累增二極體 (Single Photon Avalanche Diode, SPAD) 是利用元件操作在高於崩潰電壓之偏壓下，光子被吸收進而觸發衝擊游離機制，產生大量崩潰載子，因此可偵測極為微弱光。砷化銦鎵/砷化銦鋁單光子累增二極體以砷化銦鎵作為吸收層吸收光子，砷化銦鋁則作為累增層；其中，累增層材料由較早開始研究的磷化銦(InP)改為砷化銦鋁是因為它具備以下的特性：在相同的厚度下，崩潰電壓有較好的溫度穩定性；另砷化銦鋁有較高的累增觸發機率，預期能有較高的光偵測效率，故本研究採用砷化銦鋁作為累增層。元件採正面收光且分離吸收層、漸變層、電荷層、累增層(separate absorption, grading, charge and multiplication, SAGCM)的平台式結構，優化電荷層的摻雜濃度，使得累增層的電場大於崩潰閥值同時又能讓吸收層被空乏產生擊穿效應。我們製作出兩種不同電荷層濃度的SPAD元件，在室溫下的崩潰電壓都約為47伏，擊穿電壓約為25伏；溫度係數在200 K以下斜率約為50 mV/K；SPAD元件以閘控模式電路操作以降低二次崩潰的影響；暗計數率在187.5 K下、超額偏壓0.1 %下約為5×106 counts per second，並且由暗計數變溫結果可得其活化能遠小於吸收層材料能隙中心，因此暗計數主要由側壁的表面缺陷所主導，這導因於元件保護層品質不佳，遂亦使得在100 μs的hold off time的操作下仍有45 %的二次崩潰機率；另透過調整電荷層摻雜濃度可在過量偏壓5 %的條件下使光偵測效率增加。論文最後亦透過崩潰訊號對時間以及元件電容-對時間之可靠度分析，探究元件特性欠佳之因素，其可歸因於崩潰載子被保護層缺陷捕捉從而使寄生電容上升，這會導致崩潰訊號不斷隨時間上升，造成極不穩定的計數率。 ;Single Photon Avalanche Diode (SPAD) is used to detect low power light via absorbing single photon and generating carriers to induce impact ionization process. The device under investigation is InGaAs/InAlAs SPAD using InGaAs as the absorption layer and InAlAs as the multiplication layer. InAlAs, as compared to InP, has the following characteristics of better temperature stability of breakdown voltage upon the same thickness of multiplication layer and theoretically higher photon detection efficiency due to higher avalanche trigger probability. As a result, we use InAlAs as the multiplication layer. The SPADs with top-illuminated, mesa-type, and separation absorption, grading, charge and multiplication (SAGCM) structure are studied. To The proper control of the charge layer doping helps to fully deplete the absorption layer with high enough electric field and to avoid the tunneling current with low enough electric field. We fabricated SPADs with two different charge layer dopings and their current-voltage characteristics are measured. The breakdown voltage and punch-through voltage at room temperature for both SPADs are about 47 volts and 25 volts, respectively. The temperature coefficients of the breakdown voltages are around 50 mV / K below 200 K. SPAD is operated in a gated mode for suppressing the afterpulsing effect. The dark count rate (DCR) of 5×106 is measured at 187.5 K and excess bias of 0.1 %. From the curve of DCR versus temperature, the activation energy is obtained to be well below the half bandgap of InGaAs layer, which manifests that the DCR is mainly originated from the surface defect of sidewall due to the poor quality of passivation layer. This also results a higher afterpulsing probability of 45 % even under the hold-off time of 100 μs. In another hand, the photon detection efficiency can be improved by properly adjusting the charge layer doping. In the last, we study the performance degradation of SPAD by measuring the amplitude of avalanche signal and the device capacitance versus time. The increase of amplitude of avalanche signal and device capacitance with time is attributed to the trapping of avalanche carriers within the passivation layer, resulting very unstable count rate.
Appears in Collections:	[Graduate Institute of Electrical Engineering] Electronic Thesis & Dissertation

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