DFB Laser

At the Integrated Optoelectronic Device Lab (IOED), we develop advanced Distributed Feedback (DFB) laser chips for high‑speed optical communications, silicon photonics, and LiDAR systems. Through meticulous design and rigorous manufacturing, our team has achieved significant advances across these domains.

For high‑speed optical communications, our 1.31‑μm directly modulated DFB lasers have demonstrated data rates up to 53.12 Gb/s (PAM‑4) with stable single‑frequency operation and low threshold currents, ideal for next‑gen 200/400 Gb Ethernet links.

In LiDAR, our C‑band DFB lasers feature exceptionally low RIN and sub‑100 kHz linewidth with sufficient optical power for FMCW. Our 1.55‑μm high‑power DFBs have produced pulsed optical power up to 6 W and more than 100 mW CW with GHz‑class modulation, suitable for LEO optical links and long‑reach communications.

DFB device structures and characterization — Representative DFB structures and characterization.

High‑speed and spectral performance — High‑speed transmission and spectral performance.

GaN, SiC, Si material property comparison — Fig. 1 Comparison of GaN, SiC, and Si material properties.

Power device characteristic comparison — Table 1 Characteristics of different semiconductor materials.

2022–2028 GaN power device market forecast — Fig. 2 2022–2028 market forecast for GaN power devices.

GaN HEMT & MMIC

Wide‑bandgap semiconductors enable lower switching loss and higher efficiency at elevated switching frequencies. Power‑device figures of merit (e.g., R_ON·Q_gd) and Johnson’s FOM both favour GaN for high‑frequency power conversion.

We develop high‑frequency GaN HEMTs and MMICs, achieving f_T > 95 GHz and f_max > 150 GHz via advanced T‑gate processes and precision RF characterization.

T‑gate device micrograph and frequency response — Fig. 3 (a) T‑gate OM; (b) cross‑section; (c) gain‑frequency performance.

Light‑Emitting Transistor

The LET originated from UIUC (Holonyak Jr. & Feng), leveraging radiative recombination in graded‑base InGaP/GaAs HBTs. Embedding QWs in the base yields high‑speed three‑port electro‑optical operation; with cavity and confinement, QW‑HBTs evolve into transistor lasers (TLs) with resonance‑free, wideband responses via intracavity photon‑assisted tunneling.

IOED advances LET/TL efficiency through epi design, layout, process, and electro‑optical characterization. In collaboration with UIUC, we pursue EPICs (Electron‑Photonic Integrated Circuits) for future systems.

Timeline of LET‑based optoelectronics — Fig. 1 LET‑based optoelectronics developments and milestones.

Fig. 2 Device cross‑section and SEM photo.

Fig. 1 LED landscape (2018), Yole Development.

Micro‑LED

Micro‑LED arrays deliver outstanding contrast, response time, and energy efficiency relative to LCD and OLED. Their inorganic emitters provide long lifetimes and high luminance with minimal risk of burn‑in.

Sub‑nanosecond responses enable AR/VR, ultra‑high‑speed links, and VLC. IOED optimizes epi‑layers, surface treatments, and ALD passivation, and develops high‑speed micro‑LEDs for VLC with rigorous electro‑optical characterization.

Silicon Photonics

Silicon photonics has scaled from thousands to millions of integrated devices in data‑center transceivers, with sensing and computing on the horizon. Heterogeneous integration and CPO enable EPICs that merge optics with electronics for system‑level efficiency.

Leveraging VCSEL/DFB/LED/HEMT/HBT expertise, IOED designs SiPh chips integrated with DFB lasers for narrow‑linewidth QKD sources and develops SSC‑integrated high‑power DFBs for efficient fiber/SiPh coupling.

SiPh chip with integrated DFB for QKD — Fig. 1 SiPh chip integrating DFB for QKD narrow‑linewidth source.

Fig. 2 SSC‑integrated high‑power DFB schematic.

VCSEL

VCSELs emit normal to the wafer surface, enabling compact footprints, low power, and precise wavelength control for data communications, optical interconnects, 3D sensing, LiDAR, and biomedical systems. IOED advances VCSEL design, process integration, and performance to meet emerging requirements.

SPAD

Single‑Photon Avalanche Diodes (SPADs) operate above breakdown in Geiger mode; single carriers trigger self‑sustained avalanches, yielding effectively infinite gain for single‑photon sensitivity.

IOED studies III‑V and Ge‑on‑Si SPADs in the C‑band, optimizing structures via TCAD, quenching circuits, and low‑noise measurement to raise PDE, suppress DCR/afterpulsing, and reduce timing jitter. We collaborate with TSMC toward CMOS‑compatible Ge‑on‑Si SPADs for LiDAR and optical links.

SPAD operation and structures — Geiger‑mode operation and device structures.

SPAD measurements and curves — Measurement setups and key characteristics.

Fig. 1 Common HBT schematic and band diagram.

Fig. 2 Type‑I/II DHBT issues and mitigations.

Two‑port model and S‑parameter curves — Fig. 3 Two‑port model, small‑signal circuit, and S‑parameter data.

HBT

As wireless systems migrate to mmWave/sub‑THz, InP devices offer higher mobility and power density than GaAs, enabling efficient 5G/6G power amplification, satellite RFICs, and long‑range sensing. IOED develops high‑frequency InP HBTs with sub‑500 nm emitters via e‑beam lithography and self‑aligned processes to reduce parasitics and boost transit frequency and PAE.

Research