Charge Control Layer Research Articles

Reliability Scaling of Nanoscale Avalanche Photodiodes in High-Speed Optical Communication

In the present era of big data and 5G wireless, both microelectronic and photonic components are indispensable building blocks. For microelectronics, device miniaturization has been following Moore’s law to attain higher speed and greater functionality. For photonics, similar device scaling is also evolving in both lasers and photodiodes to transmit high data rates of 25 Gb/s and beyond. However, such device miniaturization may impose challenges such as reliability and fabrication that require careful scientific and engineering studies. In particular, the reliability understanding of photonic device scaling is fairly rudimentary with only scattered reports. In this paper, we study the device and reliability scaling of nanoscale avalanche photodiodes (APDs). The device miniaturization of APDs mainly involves thickness reduction in the charge control and multiplication layers. The layer reduction however causes an increase in breakdown field that may adversely affect reliability in several aspects such as electrical/optical overload and electrostatic discharge (ESD). We present a new reliability degradation model of APDs based on the breakdown field and correlate it with the experimental data. Empirical reliability equations are instituted to establish quantitative formulation. We discuss the overload and ESD performances as a function of breakdown field for both planar-type and mesa-type APD structures.

Ultrathin PVK charge control layer for advanced manipulation of efficient giant CdSe@ZnS/ZnS quantum dot light-emitting diodes

Abstract An efficient green quantum dot light-emitting diode (QLED) consisted of giant CdSe@ZnS/ZnS quantum dots (QDs) with the gradient composition was reported. The electroluminescence (EL) enhancement was demonstrated by utilizing a poly(9-vinlycarbazole) (PVK) charge control layer (CCL) to regulate the injection charge inside QD emitters. With lower electron mobility and high triplet energy for the possibility of efficient resonance energy transfer, the ultrathin PVK CCL possessed the capability of increasing the radiative recombination of excitons by reducing the predominant electrons, adjusting the charge injection rate, and thus suppressing QD charging effect. As a consequence, the QLED with a CCL demonstrated excellent performance (external quantum efficiency (EQE) ∼ 4.3% and maximum luminance (Lmax) ∼41900 cd/m2) superior to that of previously published Type-II″ devices with similar organic/polymer carrier transporting materials. Furthermore, neither noticeable increase of turn-on voltage nor photon emission from PVK were observed after inserting this PVK CCL in right position. This demonstration creates a new route to design impact QLED architecture for next generation displays.

4H-SiC SACM Avalanche Photodiode With Low Breakdown Voltage and High UV Detection Efficiency

In this paper, a high-performance 4H-SiC separated absorption charge multiplication ultraviolet avalanche photodiode (APD) with low breakdown voltage is designed and fabricated. The room temperature dark current of the APD remains at ∼0.1 pA level ( $\rm{\sim}29\;\text{pA/ cm}^{- 2}$ ) when reverse bias is below 50 V and then rises by several orders of magnitude before avalanche breakdown occurs. An avalanche gain up to 106 is achieved at 67 V. Based on secondary ion mass spectroscopy measurement, the electric field distribution within the as-fabricated APD is numerically simulated. The ionization ratio of Al in the p-type charge control layer is estimated to be 40%. The frequency dispersion phenomenon in capacitance–voltage (C-V) measurement should be caused by structural defects existing within the APDs, which may also be the source of the enhanced dark current before avalanche breakdown. The room-temperature maximum quantum efficiency is ∼80% at 270 nm with an ultraviolet (UV)/visible rejection ratio more than 10 4.

Effect of broad recombination zone in multiple quantum well structures on lifetime and efficiency of blue organic light-emitting diodes

Blue phosphorescent organic light-emitting diodes with multiple quantum well (MQW) structures (from one to four quantum wells) within an emitting layer (EML) are fabricated with charge control layers (CCLs) to control carrier movement. The distributed recombination zone and balanced charge carrier injection within EML are achieved through the MQW structure with CCLs. Remarkably, the half-decay lifetime of a blue device with three quantum wells, measured at an initial luminance of 500 cd/m2, is 3.5 times longer than that using a conventional structure. Additionally, the device’s efficiency improved. These results are explained with the effects of triplet exciton confinement and triplet–triplet annihilation within each EML.

The effect of a charge control layer on the electroluminescent characteristic of blue and white organic light-emitting diodes.

We investigated blue fluorescent organic light-emitting diode (OLED) with a charge control layer (CCL) to produce high efficiency and improve the half-decay lifetime. Three types of devices (device A, B, and C) were fabricated following the number of CCLs within the emitting layer (EML), maintaining the thickness of whole EML. The CCL and host material, 2-methyl-9,10-di(2-naphthyl)anthracene, which has a bipolar property, was able to control the carrier movement with ease inside the EML. Device B demonstrated a maximum luminous efficiency (LE) and external quantum efficiency (EQE) of 9.19 cd/A and 5.78%, respectively. It also showed that the enhancement of the half-decay lifetime, measured at an initial luminance of 1,000 cd/m2, was 1.5 times longer than that of the conventional structure. A hybrid white OLED (WOLED) was also fabricated using a phosphorescent red emitter, bis(2-phenylquinoline)-acetylacetonate iridium III doped in 4,4'-N,N'-dicarbazolyl-biphenyl. The property of the hybrid WOLED with CCL showed a maximum LE and an EQE of 13.46 cd/A and 8.32%, respectively. It also showed white emission with Commission International de L'Éclairage coordinates of (x = 0.41, y = 0.33) at 10 V.

Improved efficiency and lifetime for green phosphorescent organic light-emitting diodes using charge control layer

We investigated green phosphorescent organic light-emitting diodes (PHOLEDs) with charge control layer (CCL) to produce high efficiency and improve operational lifetime. Three types of devices were fabricated following the number of CCL within emitting layer (EML), maintaining the thickness of whole EML. The CCL and host material, which was 4,4′-bis (carbazol-9-yl)biphenyl (CBP) with bipolar property, can control carrier movement in EML. Therefore, the electroluminescent (EL) performance improvement as efficiency and lifetime was realized with a good charge balance, an effective triplet exciton confinement, and the reduced triplet exciton quenching effect in EML. Device 2 with a CCL as exciton distribution structure exhibits the remarkable EL performances for the maximum luminous and external quantum efficiency of 65.34cd/A and 20.42%, respectively. Moreover, operational lifetime is nearly improved 2.5 times than the conventional device.

插入电荷控制层对蓝色OLED发光性能的提高

The performance of blue fluorescent organic light-emitting device(OLED) with N6,N6,N12,N12-tetrap-tolylchrysene-6,12-diamine(DNCA) as emitting layer(EML) was improved by inserting 2-methyl-9,10-di(2-napthyl) anthracene(MADN) 9,10-di(2-naphthyl) anthracene(ADN) as charge control layers(CCLs) into the device.For the optimum device with CCL structure of ITO/NPB(40 nm)/DNCA(15 nm)/MADN(3 nm)/DNCA(15 nm)/ADN(3 nm)/Bphen(30 nm)/LiF(0.8 nm)/Al(120 nm),the maximal current efficiency of 5.6 cd/A and the maximal luminance of 23 310 cd/m2were achieved,which were enhanced by 70% and 87%comparing with the control device(CD) without CCLs,respectively.The performance improvement of the device can be attributed to the synergistic action(function) of the two CCLs.By utilizing the CCL structure,the original emitting zone can be separated into two parts by inserting MADN in the first EML,and the exciton formation region can also be broadened accordingly.Therefore,the exciton's radiative process can be utilized to a great extent.Meanwhile,the holes can be effectively confined in the second EML by inserting ADN between the EML and ETL,which can prevent the exciton's non-radiative process in the ETL so as to improve the device performance.

Effect of a multiple quantum well structure as an emissive layer based on blue phosphorescent organic light-emitting diodes

We demonstrate a multiple quantum well (MQW) structure with charge control layers (CCLs) to produce highly efficient blue phosphorescent organic light-emitting diodes (OLEDs). Three types of devices (A, B, and C) were fabricated with the following emitting layer structures while maintaining the thickness of the EMLs: host-emitter doping layers, nondoping layers, and CCLs. Triplet energies in such MQW devices were confined at the EMLs. The properties of a device with an MQW demonstrated a maximum luminous efficiency and external quantum efficiency of 18.33 cd/A and 9.47%, respectively. The device also showed a reduction in the turn-on voltage from 3.5 V to 2.5 V and an enhancement of the power efficiency. The described MQW device concept is considered to be useful for future OLED displays and light applications.

Efficiency of a blue organic light-emitting diode enhanced by inserting charge control layers into the emission region

We demonstrate high current efficiency of a blue fluorescent organic light-emitting diode (OLED) by using the charge control layers (CCLs) based on Alq3. The CCLs that are inserted into the emitting layers (EMLs) could impede the hole injection and facilitate the electron transport, which can improve the carrier balance and further expand the exciton generation region. The maximal current efficiency of the optimal device is 5.89 cd/A at 1.81 mA/cm2, which is about 2.19 times higher than that of the control device (CD) without the CCL, and the maximal luminance is 19.660 cd/m2 at 12 V. The device shows a good color stability though the green light emitting material Alq3 is introduced as the CCL in the EML, but it has a poor lifetime due to the formation of cationic Alq3 species.

P-type interface charge control layers for enabling GaN/SiC separate absorption and multiplication avalanche photodiodes

A p-type interface charge control layer (PICCL) is introduced that enables optimization of the net positive polarization induced interface charge at the GaN/SiC interface in GaN/SiC separate absorption and multiplication avalanche photodiodes (SAM-APDs) by varying its thickness. The response from SAM-APDs with PICCL thickness less than 10 nm has an anomalous shape at all bias attributed to the collection of carriers generated directly in the SiC layer. Devices with a 15 nm thick PICCL exhibit GaN related response at high bias that is indicative of punch-through of the electric field into the GaN absorption region due to optimization of the net interface charge.

Highly Efficient Blue- and White-Organic Light-Emitting Diode Based on Dual Recombination Zones with a Charge Control Layer

Highly efficient blue phosphorescent organic light-emitting diodes are investigated using iridium(Ill) bis[(4,6-di-fluorophenyl)-pyridinato-N,C2']picolinate doped in N,N'-dicarbazolyl-3,5-benzene (mCP) with a charge control layer (CCL) as the dual recombination zone (DRZ) system. DRZ with CCL was used to form a broad recombination zone and exciton confinement within each emission zone. Holes and electrons can be easily transported through the CCL, which were a mixed p-type mCP and n-type 2,2',2"-(1,3,5-benzenetryl) tris(1-phenyl)-1H-benzimidazol, for controlling the carrier movement. The CCL can play a role in triplet exciton blocking as expected from high triplet energy levels as well. Additionally, a white organic light-emitting diode was fabricated using a new phosphorescent orange emitter: bis[2-(2,4-difluorophenyl)pyridinato]iridium 2-(2-hydroxyphenyl)benzothia zolate doped in DRZ. The white device showed a maximum luminous efficiency of 23.15 cd/A, a maximum external quantum efficiency of 9.56%, and a maximum power efficiency of 13.37 lm/W. It also showed white emission with CIEx,y coordinates of (x = 0.33, y = 0.41) at 8 V.

Enhanced life time and suppressed efficiency roll-off in phosphorescent organic light-emitting diodes with multiple quantum well structures

We demonstrate red phosphorescent organic light-emitting diodes (OLEDs) with multiple quantum well structures which confine triplet exciton inside an emitting layer (EML) region. Five types of OLEDs, from a single to five quantum wells, are fabricated with charge control layers to produce high efficiencies, and the performance of the devices is investigated. The improved quantum efficiency and lifetime of the OLED with four quantum wells, and its suppressed quantum efficiency roll-off of 17.6%, can be described by the increased electron–hole charge balance owing to the bipolar property as well as the efficient triplet exciton confinement within each EML, and by prevention of serious triplet–triplet and/or triplet–polaron annihilation as well as the Förster self-quenching due to charge control layers.

Effect of triplet multiple quantum well structures on the performance of blue phosphorescent organic light-emitting diodes

We investigate multiple quantum well [MQW] structures with charge control layers [CCLs] to produce highly efficient blue phosphorescent organic light-emitting diodes [PHOLEDs]. Four types of devices from one to four quantum wells are fabricated following the number of CCLs which are mixed p- and n-type materials, maintaining the thickness of the emitting layer [EML]. Remarkably, such PHOLED with an optimized triplet MQW structure achieves maximum luminous and external quantum efficiency values of 19.95 cd/A and 10.05%, respectively. We attribute this improvement to the efficient triplet exciton confinement effect and the suppression of triplet-triplet annihilation which occurs within each EML. It also shows a reduction in the turn-on voltage from 3.5 V (reference device) to 2.5 V by the bipolar property of the CCLs.

III-NITRIDE/SiC SEPARATE ABSORPTION AND MULTIPLICATION AVALANCHE PHOTODIODES: THE IMPORTANCE OF CONTROLLING POLARIZATION-INDUCED INTERFACE CHARGE

A III-Nitride/ SiC separate absorption and multiplication avalanche photodiode (SAM-APD) offers a novel approach for fabricating high gain photodetectors with tunable absorption over a wide spectrum from the visible to deep ulltraviolet. However, unlike conventional heterojunction SAM APDs, the formation of polarization-induced charge at the hetero-interface arising from spontaneous and piezoelectric polarization can dramatically affect the performance of this detector. In this paper we report on the role of this interface charge on the performance of GaN / SiC SAM APDs. Simulations of the electric field profile within this device structure while biased near avalanche breakdown indicate that the density of positive interface charge may be sufficient to confine the electric field within the SiC multiplication region with negligible punch-through into the GaN absorption region, a distribution that is likely undesirable for efficient collection of photo-generated holes due to the presence of defects at the hetero-interface. Simulations further show that the incorporation of a p -type doped interface charge control layer at the hetero-interface can modify the total density of charge at the interface and allow for the tailoring of the electric field profile within this device. Experimental results are provided that correlate well with the simulation results.

Efficient multiple triplet quantum well structures in organic light-emitting devices

We demonstrate the multiple quantum well (MQW) structures with the charge control layers (CCLs) to produce highly efficient red phosphorescent organic light-emitting devices (OLEDs). Various triplet quantum well devices from a single to five quantum wells are realized using wide band-gap hole and electron transporting layers, narrow band-gap host and dopant materials, and CCLs. Triplet energies in such MQW devices are confined at the emitting layers. The maximum external quantum efficiency of 14.8% with a two quantum well device structure is obtained. The described MQW device concept has been proposed to be very useful to future OLED display and lighting applications.

Effect of impact ionization in the InGaAs absorber on excess noise of avalanche photodiodes

The effects of impact ionization in the InGaAs absorption layer on the multiplication, excess noise and breakdown voltage are modeled for avalanche photodiodes (APDs), both with InP and with InAlAs multiplication regions. The calculations allow for dead space effects and for the low field electron ionization observed in InGaAs. The results confirm that impact ionization in the InGaAs absorption layer increases the excess noise in InP APDs and that the effect imposes tight constraints on the doping of the charge control layer if avalanche noise is to be minimized. However, the excess noise of InAlAs APDs is predicted to be reduced by impact ionization in the InGaAs layer. Furthermore the breakdown voltage of InAlAs APDs is less sensitive to ionization in the InGaAs layer and these results increase tolerance to doping variations in the field control layer.

Electrophorectic Self Assembly, A Manufacturing Process for Various Industries

Electrophoretic Self Assembly (ESA) is the name for a manufacturing process where large, functional particles (hundreds of microns) are imaged or properly placed using the electrical forces found in the electrophotographic imaging process. The functional particles are the “toners”, in this case liquid toners; and the imaging surface is a fixed configuration printing plate or the traditional optically addressable plate.A typical use for this technology is the high volume manufacture of RFID(radio frequency identification tags). Silicon die of the order 400x400x50 micron in dimension needs to be accurately placed in X & Y; rotated in alignment with the x axis, and oriented (heads vs tails) or correct side up. For commercial success this needs to be done quickly and at cost levels approaching the graphic art industry. I will describe experiments in which silicon die is coated (one side) with a charge control layer, which when dispersed in an Isopar diluent (containing a suitable charge director); will impart are suitable ionic charge to the die. This will allow it to be placed, rotated and oriented on a suitable substrate.The presentation will report progress in this endeavors and include calculations of the expected imaging forces and a limit to the largest die than can be imaged. Other possible commercial applications will be discussed.

Dipole heterostructure field-effect transistor

It is proposed to reduce the gate current by using a dipole created by two doped planes, n/sup ++/ and p/sup ++/, in charge control layer, dipole heterostructure field-effect transistors (dipole HFETs) fabricated in AlGaAs/GaAs use doped p/sup ++/ and n/sup ++/ planes in the charge control AlGaAs layer to form a dipole that provides a considerably larger barrier between the channel and the gate than that in conventional heterostructure FETs. This leads to a reduction of the forward-biased gate current in enhancement-mode n-channel devices, by a factor of approximately 9 at 1.2 V in the experimental devices, when compared with equivalent conventional HFETs. A much broader transconductance region, in the range of 0.5-2.5-V gate bias, a higher maximum drain current, and no negative transconductance are also observed. A comparison between the gate current-voltage characteristics of conventional and dipole HFETs for 1- mu m-long and 10- mu m-wide gate devices is given. The measured results clearly indicate that a dipole HFET has a much smaller gate leakage current leading to superior performance of enhancement-mode devices. The results demonstrate the effectiveness of the dipole layer concept for digital HFET devices. >

Heterostructure field effect transistor with doping dipole in charge control layer

The heterostructure field effect transistors with a doping dipole layer obtained by planar p++ and n++ layers in charge control layer are proposed and fabricated in AlGaAs/GaAs. The dipole creates a large barrier between the channel and the gate, and this leads to a reduction of the forward biased gate current, a broad transconductance peak, a high maximum drain current, and no negative transconductance in enhancement-mode n-channel devices.

0.5- mu m gate length self-aligned gate MODFET with reduced short-channel effects

Reduced short-channel effects were obtained by using a buried AlGaAs layer beneath the channel. A 0.5*10- mu m/sup 2/ MODFET was fabricated that had a peak transconductance of 264 mS/mm with a K-factor of 425 mA/V/sup 2/-mm. The measured output conductance was 2.37 mS/mm, a reduction from 18 mS/mm for a 0.5- mu m device without the buried layer. This combination of high transconductance and low output conductance makes the device ideal for high-speed analog and digital applications. The reduced output conductance gives a maximum gain of 110, compared with a more typical gain of 25 for a standard 0.5- mu m MODFET device. Threshold voltage dependence on gate length decreases from a 60-mV shift for 1.5- to 0.5- mu m gate length to 20 mV over the same range. The structure of the device, which was grown by molecular-beam epitaxy, consists of a five-period AlGaAs/GaAs superlattice and AlGaAs cap and spacer layers. The GaAs conducting channel is located between this charge control layer and a buried AlGaAs channel confinement buffer layer. This double heterostructure forms a quantum well in the channel region to further confine the quasi-two-dimensional electron gas. >