High-power InAlAs/InGaAs Schottky barrier photodiodes for analog microwave signal transmission

The design, manufacturing and DC and microwave characterization of high-power Schottky barrier InAlAs/InGaAs back-illuminated mesa structure photodiodes are presented. The photodiodes with 10 and 15 μm mesa diameters operate at ≥40 and 28 GHz, respectively, have the output RF power as high as 58 mW at a frequency of 20 GHz, the DC responsivity of up to 1.08 A/W depending on the absorbing layer thickness, and a photodiode dark current as low as 0.04 nA. We show that these photodiodes provide an advantage in the amplitude-to-phase conversion factor which makes them suitable for use in high-speed analog transmission lines with stringent requirements for phase noise.

Постростовые технологии каскадных фотоэлектрических преобразователей на основе A-=SUP=-3-=/SUP=-B-=SUP=-5-=/SUP=--гетероструктур

Investigation and development of the post-growth technology for fabricating multi-junction photovoltaic converters based on GaInP/GaInAs/Ge heterostructure has been carried out. Antireflection coating, ohmic contacts and mesa-structure forming stages have been reviewed. The technology of n+-GaAs contact layer etching with the help of plasma-chemical, liquid and ion-beam etching has been investigated. Antireflection coefficient of radiation from the heterostructure with TiOx/SiO2 (x close to 2) antireflection coating surface was less then 3% in wavelength range 450-850 nm. The value of contact resistance for n- and p-type conductivity was 3E−5 − 3E−6 ohm · cm2, the decrease of photosensitive region shading degree at increased bus-bar conductivity has been archived. The mesa-structure surface current leakage decreased to the value of E-9 A at voltage less then 1 V.

GaN-Based PCSS with High Breakdown Fields

The suitability of GaN PCSSs (photoconductive semiconductor switches) as high voltage switches (>50 kV) was studied using a variety of commercially available semi-insulating GaN wafers as the base material. Analysis revealed that the wafers’ physical properties were noticeably diverse, mainly depending on the producer. High Voltage PCSSs were fabricated in both vertical and lateral geometry with various contacts, ohmic (Ti/Al/Ni/Au or Ni/Au), with and without a conductive n-GaN or p-type layer grown by metal-organic chemical vapor deposition. Inductively coupled plasma (ICP) reactive ion etching (RIE) was used to form a mesa structure to reduce field enhancements allowing for a higher field to be applied before electrical breakdown. The length of the active region was also varied from a 3 mm gap spacing to a 600 µm gap spacing. The shorter gap spacing supports higher electric fields since the number of macro defects within the device’s active region is reduced. Such defects are common in hydride vapor phase epitaxy grown samples and are likely one of the chief causes for electrical breakdown at field levels below the bulk breakdown field of GaN. Finally, the switching behavior of PCSS devices was tested using a pulsed, high voltage testbed and triggered by an Nd:YAG laser. The best GaN PCSS fabricated using a 600 µm gap spacing, and a mesa structure demonstrated a breakdown field strength as high as ~260 kV/cm.

К 125-летию со дня рождения лауреата Нобелевской премии академика Николая Николаевича Семенова Архитектура мезы и эффективность InGaP/Ga(In)As/Ge солнечных элементов

It has been shown that the mesa architecture and achieved quality of the mesa sidewall of concentrator multijunction solar cells ensured increasing their efficiency up to 36.7% at the sunlight concentration before 100 (AMO; 0.136W/cm²). Creation of the mesa structure architecture with following separation of epitaxial plates of monolithic InGaP/GaAs/Ge nanoheterostructure into chips was carried out by single step chemical wet etching in the HBr:H2O2:H2O (8:1:100) through a photoresist mask to the depth of 12-18µm. Conditions of single step etching, which ensure formation of a smooth and even side surface of the InGaP/Ga(In)As/Ge nanoheterostructure mesa containing different in composition and thickness layers have been determined. Determination of the activation energy has shown that etching occurs in the diffusion region of the heterogeneous process. In raising etchant temperature from 2 to 36˚C, a change of the tilt angle in the Ge substrate region from 4.5 to 25 angular degrees is observed, what allows optimizing the amount of concentrator solar cells and their quality at final mechanical separation of the epitaxial plate into chips.

Плазмохимическое и жидкостное травление в постростовой технологии каскадных солнечных элементов на основе гетероструктуры GaInP/GaInAs/Ge

Investigation and development of a separating mesa-structure creating technology for fabricating multi-junction solar cells based on the GaInP/GaInAs/Ge heterostructure has been carried out. Studied were methods of etching of heterostructure layers: liquid chemical etching in the etchants based on HBr, H2O2, K2Cr2O7 and plasma-chemical etching in the stream of operating gas BCl3. The comparative analysis of etching methods was studied. The protective masks based on photoresist layer and TiOx/SiO2 were developed. Multi-junction solar cells with low parameters of leakage current less than 10-7 A at voltage 0,5-1 V were created.

Грибовидная меза-структура для лавинных фотодиодов на гетероструктурах InAlAs/InGaAs

Mushroom mesa structure for InAlAs/InGaAs avalanche photodiodes (APD) was proposed and investigated. APD heterostructrures were grown by molecular-beam epitaxy. Fabricated APDs with sensitive area diameter of about 30 micron were passivated by SiN deposition and demonstrate avalanche breakdown voltage Vbr ~ 70-80 V. At applied bias of 0.9 Vbr the dark current was ~ 75-200 nA. The single-mode coupled APDs demonstrate responsivity at a gain of unity is high than 0.5A/W at 1550 nm.

The Study of High Breakdown Voltage Vertical GaN-on-GaN p-i-n Diode with Modified Mesa Structure

In this paper, we fabricated Gallium Nitride (GaN) vertical p-i-n diodes grown on free-standing GaN (FS-GaN) substrates. This homogeneous epitaxy led to thicker GaN epi-layers grown on the FS-GaN substrate, but a high crystalline quality was maintained. The vertical GaN p-i-n diode showed a low specific on-resistance of 0.85 mΩ-cm2 and high breakdown voltage (BV) of 2.98 kV. The high breakdown voltage can be attributed to the thick GaN epi-layer and corresponds to the mesa structure. Improvement of the device characteristics by the mesa structure was investigated using device simulations. We proved that a deeper mesa depth is able to decrease the electric field at the bottom of the mesa structure. Furthermore, a smaller mesa bevel angle will assist the BV up to 2.98 kV at a 60° bevel angle. Our approach demonstrates structural optimization of GaN vertical p-i-n diodes is useful to improve the device performance.

Evaluation of Surge Reduction Performance of a SiC Avalanche Diode with Mesa Structure in a Switching Power Supply

A p-n junction diode with mesa structure by silicon carbide (SiC) has been developed to utilize the avalanche breakdown in an excessed reverse bias condition to clamp the surge voltage in switch-mode power supplies. Static voltage-current correlation by pulsed reverse voltage has been measured. The increase of the breakdown voltage was measured to be 32 volts with increased current density up to 3900 A/cm2. The operational performance in suppressing the surge voltage in a step-down DC/DC converter has been evaluated. A superior performance in suppressing the surge voltage by the SiC p-n junction diode has been confirmed. It was also found that a resonant oscillation induced during clamping period limits the performance. By a circuit analysis with an equivalent circuit model, it was found that a parasitic wiring inductance between the diode and switching element induces the resonance. It was also found that a promising way to mitigate the disturbing effect is to minimize the inductance.