Special Sessions

Abstract

Session Moderator: Ms. Suma Varughese, Director General MED & CoS (Micro Electronic Devices and Computational Systems & Cyber Systems), DRDO

1. Present Status of Indigenous Technologies
2. Laser Technology
3. InP HEMT and THz: launch pad for networking in space
4. Infrared Focal Plane Array Technologies-HgCdTe & State of the Art
5. High Efficiency III-V Triple junction Solar cell for space application
6. Silicon Carbide Devices: Enabling Efficient Power Electronics for a Sustainable Future
7. GaN technology for Ka-band: Key challenges and prospects

• Present Status of Indigenous Technologies:
  Future defence systems and space technologies focus on the application of information technology and computer networking to get the advantage by using of EO systems in areas like sophisticated 3D visualisation, laser radars, and infrared sensors. This provides the defence forces with a better situational awareness and Improvement of surveillance and military ISR capabilities. Developing these systems require material and device technologies for Tuneable detectors and tuneable sources like QCL, VCSEL, DFB, T2SLbased detectors and APD. Similarly, RF sensors which remains largely concealed and shrouded in secrecy are required to work in higher frequencies with technologies like  GaN Ka band and InP based THz sources and detectors. These technologies owing to its broadband operation and enhanced reliability find application in futuristic defense systems. These technologies have begun making inroads into the SatCom market, leveraging  high efficiency compared to other materials to enable smaller device sizes, thereby saving valuable space at the system level.  Transitioning from L/C/X-bands to Ku/Ka-bands enables higher data rates in mobile satellite communication. SiC power devices and high efficiency solar cells are  technologies for green energy required both for defence and space applications.  This special session will give insight into all the above mentioned technologies along with the indigenous status.

• Laser Technology: Dr. Soma S Mahajan:
  SSPL Delhi is involved in the development of high power laser diodes. Over the years, various laser diode technologies have emerged including single emitter laser diodes, arrays, stacks and fiber coupled laser diodes (FCLD) in different operational modes and varied output powers employed for defence applications ranging from range finders, dazzelers, proximity fuses, fencing, explosive initiation for detonation etc. Recently, fabrication of indigenous laser diode technology has successfully been established at GAETEC, Hyderabad, a pilot production plant which is now capable of production of single emitter laser diode technology upto 10W (CW) for 976 nm emission. The 10W single emitters serve as the basic building blocks for high power Fiber coupled laser diodes (FCLDs) modules employed for Directed Energy Weapons (DEW) applications and initiation of explosive detonation. These modules with output power upto 100W(CW) emitting at 976 nm have also been developed in collaboration with industry. Communication between various underwater entities like submarine to unmanned underwater vehicle (UUV) is a key area for strategic defence applications in blue-green laser region of spectrum. To cater the strategic demand, SSPL is also working on blue-green laser technology employing InGaN/GaN based multiple quantum well laser structures. Laser diodes emitting at 415 nm with the pulsed power upto 4W have been developed. Apart from this, SSPL is also venturing into single mode technology; development of Vertical Cavity Surface Emitting Laser (VCSEL) and Distributed Feedback (DFB) laser diodes to produce a narrow linewidth and stable output power. These special diodes exhibit wide range of applications including optical communication systems, spectroscopy, sensing and also serve as light sources in quantum sensors and quantum communication for quantum technologies. Recently, the first set of VCSEL devices delivering power of 5mW at 850 nm have been realized. The complete development cycle starting from the procurement of raw epitaxial material to device packaging and testing was successfully carried out at SSPL.

• InP HEMT and THz: Launch pad for networking in space: Dr. Mahadev Bhat K

  With the concept of miniature satellites called CubeSats and networking them in space has the potential to revolutionize the twenty first century with extremely high speed of communication in connecting the world as one, through the space and Internet of space things (IoST). Negligible absorption of THz frequency in space compared to the high molecular absorption in earths atmosphere makes the THz frequency operation very suitable for communication in space compared to ground-based applications. Very high bandwidths available in these frequency range also makes high speed data transfer possible. High Electron Mobility Transistors (HEMTs) fabricated on InP Substrate with In_xGa_1-xAs (x varying from 0.53 to 1) as channel has made this as reality with cut of frequency reaching close to 1THz. Extremely high electron mobility and electron saturation velocity of these devices make them the best suitable candidate for low noise applications as well. with low DC power consumptions and high frequency response make them aptly suitable candidates for CubeSats. Having said that, achieving the THz performance from these devices is extremely challenging with gate lengths very low gate lengths. Exploring various aspects of device technology like material layer engineering, device topological engineering and device fabrication engineering simultaneously is essential to extract the best performance from these devices. Some of the technological challenges involved will be covered in this technical presentation.

• Infrared Focal Plane Array Technologies-HgCdTe & State of the Art
  Infrared sensor arrays are of high importance for a variety of defence, scientific, and commercial applications. An important requirement for defence surveillance systems is a sensor that can provide all condition vision. IR sensors fulfil this criterion of vision through fog, haze, dust, smoke and night, since they sense the thermal energy emitted by objects as a function of their temperature and emissivity. Other requirements are high sensitivity, fast response to scene changes, thermal stability and ability to tune to various IR windows.  Mercury Cadmium telluride (HgCdTe) based semiconductor photon detectors offer all the listed advantages for IR detection. Competing technologies in mid wave infrared (MWIR) and long wave infrared (LWIR) are InSb, antimonide based type II super lattices and quantum well infrared photodetectors (QWIPS). Shortwave infrared (SWIR) sensors are made from HgCdTe and InGaAs materials. Dual band, multi-color and hyperspectral imaging are the recent applications of III generation sensors where HgCdTe and T2SL material systems are commercially viable.  Present work reports the development of HgCdTe MWIR photodiode arrays with 15µm pitch in 384×288 and 640×512 format. The FPA package consists of a two-dimensional photovoltaic infrared detector array hybridized with a Si-CMOS based Readout Integrated Circuit (ROIC) using indium bumps. The detector array performs the function of IR signal detection and ROIC consists of signal processing circuitry which collects the signal from individual detector elements and integrates the output signal to form an image.  The two-dimensional detector array is fabricated using Hg_1-xCd_xTe semiconductor material. MCT (Hg_1-xCd_xTe) epilayers with a composition of x= (0.285-0.295)±0.0005 corresponding to a cut-off wavelength of ~4.8-5.4µm at 89 K are used. The epilayers are grown in-house by LPE technique on CZT substrate. The fabrication steps for photodiode array includes common contact formation, boron implantation for junction formation, p/n-contact etching of diodes, passivation of diodes and finally the indium bump growth to provide metal contact on individual diode pixels and ROIC. The ROIC and detector array are flip-chip bonded using FCB machine. This is followed by backside thinning, antireflection (ARC) coating, wire bonding on Dewar, cooler integration and testing. The technology for IR Focal Plane Array (IRFPA) fabrication and integration is fully developed at SSPL and thermal images of room temperature scenes have been demonstrated.

• High Efficiency III-V Triple junction Solar cell for SPACE Application: Dr. Akhilesh Pandey: 
  III-V Triple junction solar cell-based devices are showing great attention world-wide due to its wide applications in spacecraft and satellite. In the space sunlight is the only high-volume energy source available and are being used to convert light energy into the electrical power. The electrical power generated by solar panel provide the power to the space craft in all phase of life. The smallest unit of the panel is the solar cell which are connected either in series or parallel or both to increase the power which are being utilized in the space craft.  Usually normal solar cell (Si, CdTe based) cannot used in the space due to moderate efficiency, limited spectral coverage and availability of high radiation. The III-V arsenide and phosphide based solar cells exhibit several advantages as compared to other solar cells in terms of cost, weight, efficiency and radiation resistance.  III-V based solar cell are the best suited in space satellites/space craft. III-V triple junction solar cell (TJSC) structure (InGaP/InGaAs/Ge) consist of three sub cell of band gap 1.88 eV (top cell), 1.4 eV -InGaAs (middle cell), 0.67eV-Ge (bottom cell). To enhance the efficiency three single sub solar cells are added in tandem manner with the help of tunnel junction.  III-V multi-junction solar cells technology offers high efficiencies as compared with traditional solar cells and have been used effectively in space applications, concentrated photovoltaics, unmanned aerial vehicle, solar powered drones etc. In this presentation lattice matched III-V triple junction solar cell (LM-TJSC) structure consist of three sub cells {InGaP (1.88eV)/InGaAs (1.4eV)/Ge (.67eV)} integrated with the highly doped tunnel junction grown by MOCVD technique have been analysed structurally and electrically. Structurers are characterized using High resolution x- ray diffraction (HRXRD), planer/cross-sectional FE-SEM and Secondary Ion mass spectroscopy (SIMS) techniques. In the (TJSC) structure layer sequence, layer thickness and doping were determined by SIMS as well as FESEM techniques. Layers composition, strain and substrate offset angle was determined by HRXRD. The TJSC structure (determined by the above characterization) have been  used to fabricate as a solar cell with the the photo conversion efficiency ~ 27-28% under AM1.5 condition.  The extracted parameters of the solar cell structure have also been used in the simulation study of the TJSC. The structural, electrical characterization and simulation study of the TJSC structure has been presented and it will be very useful to fabricate the high efficiency space solar cell devices.
• Silicon Carbide Devices: Enabling Efficient Power Electronics for a Sustainable Future: Dr. Rupesh Kumar Chaubey
  Silicon carbide (SiC) electronics is transforming various industries with its versatility. Its temperature resilience and power efficiency make it ideal for aerospace applications, particularly in avionics and propulsion systems, where it enables aircraft to perform better while reducing weight. The defense sector also benefits from SiC’s capabilities, which support mobile artillery and armored transport. Additionally, SiC-based electronics are enhancing electric vehicles by providing efficient and reliable power management, a crucial aspect in this rapidly evolving transportation sector. Furthermore, SiC electronics are being utilized in renewable energy systems, such as solar and wind power, for remote installations, and are also improving the performance of heavy machinery in demanding environments. Overall, SiC technology is contributing to increased operational readiness, better energy efficiency, and lower maintenance costs across these diverse fields.
• GaN technology for Ka-band: Key challenges and prospects: Robert Laishram
  The increasing demand for high frequency, high linearity, and cost-effective high-power amplifier (HPA) solutions at Ka-band frequencies is a key driving force behind the rapid progress in the development of GaN Ka-band HEMT RF devices. The ability of GaN technology to meet the size, weight, and power (SWaP) constraints is one of its most transformative strengths in meeting the demands of strategic systems, military radars, 5G/6G systems. However, before the full potential of the GaN can be exploited, several critical issues related to the device design, epi-structure and fabrication challenges need to be addresses. The need to aggressive scale the gate length mitigating the adverse issues related to short-channel effects, gate leakage and parasitic capacitances remains a major challenge. The talk will focus on the future prospects of this critical technology, key challenges and briefly touch upon the journey at SSPL to indigenously develop this technology.