CCD-based thermoreflectance microscopy has emerged as a high resolution, non-contact imaging technique for thermal profiling and performance and reliability analysis of numerous electronic and optoelectronic devices at the micro-scale. This thermography technique, which is based on measuring the relative change in reflectivity of the device surface as a function of change in temperature, provides high-resolution thermal images that are useful for hot spot detection and failure analysis, mapping of temperature distribution, measurement of thermal transient, optical characterization of photonic devices and measurement of thermal conductivity in thin films. In this paper we review the basic physical principle behind thermoreflectance as a thermography tool, discuss the experimental setup, resolutions achieved, signal processing procedures and calibration techniques, and review the current applications of CCD-based thermoreflectance microscopy in various devices.

https://iopscience.iop.org/article/10.1088/0022-3727/42/14/143001/pdf

CCD-based thermoreflectance microscopy: principles and applications

Double-fused vertical-cavity surface-emitting lasers (VCSELs) have demonstrated the highest temperature performance of any 1.5 μm VCSEL, but further optimization is needed to reduce their temperature sensitivity. We present and analyze threshold current measurements of these devices between −90 °C and 30 °C stage temperature. Despite a zero gain peak offset from the emission wavelength at room temperature, the pulsed threshold current has its minimum near −50 °C corresponding to about −30 nm gain offset. This is in contrast to a common VCSEL design rule. Temperature effects on the optical gain of the strain-compensated InGaAsP/InP active region are found to be the main cause for the disagreement. A design rule modification is proposed. Numerical simulation of an optimized 1.55 μm VCSEL shows that gain offset improvements are counteracted by loss mechanisms.

Minimum temperature sensitivity of 1.55 μm vertical-cavity lasers at −30 nm gain offset

We report record temperature and wavelength range attained using MOVPE-grown AlGaAs vertical cavity surface-emitting lasers (VCSEL's). Unbonded continuous-wave lasing is achieved at temperatures up to 200/spl deg/C from these top-emitting VCSEL's and operation over a 96-nm wavelength regime near 850 nm is also achieved from the same nominal design. Temperature and wavelength insensitive operation is also demonstrated; threshold current is controlled to within a factor of 2 (2.5-5 mA) for a wavelength range exceeding 50 nm and to within /spl plusmn/30% (5-10 mA) for a temperature range of 190/spl deg/C at 870 nm. >

200/spl deg/C, 96-nm wavelength range, continuous-wave lasing from unbonded GaAs MOVPE-grown vertical cavity surface-emitting lasers

Record-long emission wavelengths up to 1.3 /spl mu/m have recently been demonstrated from highly strained InGaAs-GaAs double-quantum-well (DQW) vertical-cavity surface-emitting lasers (VCSELs). The operation of InGaAs VCSELs at such long wavelengths has relied on a large detuning between the spectral positions of QW gain maximum and cavity resonance. This detuning also affects the high-temperature performance and temperature sensitivity of such devices. In this paper, we present and evaluate the threshold current-temperature characteristic of such lasers in relation to the gain-cavity detuning at room temperature (RT). For a near-zero gain peak offset from the emission wavelength at RT, the minimum threshold current is found at the temperature where the gain peak wavelength and the cavity resonance are approximately aligned. This is well in line with a common design rule for GaAs-based VCSELs. However, we show that this design rule fails in the case of larger gain-cavity misalignment at RT. Instead, a minimum threshold current is obtained considerably below the temperature of zero gain offset. We propose a conceptual model that relates the gain-cavity detuning at RT to the temperature sensitivity of the active region performance, which qualitatively describes the threshold current-temperature characteristic typical of VCSELs. The results demonstrate the importance of improving the temperature characteristic of the active region in order to reduce the high temperature sensitivity of devices with large detuning.

Temperature sensitivity of the threshold current of long-wavelength InGaAs-GaAs VCSELs with large gain-cavity detuning

A laser (20) comprises a first contact to receive an active region control signal, a second contact to receive an optical absorber control signal, and a sandwich of distributed Bragg reflector mirror stacks. Each distributed Bragg reflector mirror stack (36, 60) has an alternate doping with respect to an adjacent distributed Bragg reflector mirror stack. An active region (26) is positioned in the sandwich to provide optical gain in response to the active region control signal. An optical absorber (150) is positioned in the sandwich. The optical absorber has wavelength dependent absorption in response to the optical absorber control signal. The device of the invention may be utilized as an integrated detector, a self-pulsating laser, a high speed intracavity modulator, or an optical pick-up device.

Vertical-cavity surface-emitting laser with an intracavity quantum-well optical absorber

A systematic and comparative study of the temperature performance of vertical‐cavity surface‐emitting lasers (VCSELs) is presented to discuss how thermal effects govern their temperature range for cw operation. These include the temperature‐induced detuning of the lasing mode from the gain peak, thermal self‐heating, and thermal runaway. The power dissipation of the VCSELs and the resultant rise in junction temperature have been measured as a function of the mode detuning. It is shown that low power dissipation is achieved by aligning the cavity mode to the gain peak and introducing continuously graded heterointerfaces throughout the VCSEL structure. By selecting the optimal mode detuning, VCSELs have achieved excellent operating characteristics over a broad range of temperatures, including thermally stable threshold voltage and current, and a very wide temperature range for both pulsed (100–580 K) and continuous‐wave (100–400 K) operations.

High temperature pulsed and continuous-wave operation and thermally stable threshold characteristics of vertical-cavity surface-emitting lasers grown by metalorganic chemical vapor deposition

Latching optical switches and cascadable optical logic gates and and or are demonstrated by the monolithic integration of a vertical‐cavity surface‐emitting laser with heterojunction photothyristors. Excellent optical switching characteristics, including low switching power (tens of nW), high optical gain (≳104), and a large on/off ratio, have been achieved.

High‐performance latchable optical switch and logic gates based on the integration of surface‐emitting lasers and photothyristors

The first experimental demonstration of a surface‐normal bistable optical switching device based on the monolithic integration of a vertical‐cavity surface‐emitting laser and a pnpn photothyristor is reported. By the use of ion implantation, it is shown that the positive feedback in the photothyristor can be controlled, thus enabling the integration of both bistable and latching optical switches on the same epitaxial structure. High contrast (30 dB) and an optical gain of 8 are demonstrated.

Surface‐emitting laser‐based optical bistable switching device

Summary form only given. Room-temperature, CW operation of GaAs/AlGaAs multiple-quantum-well vertical-cavity surface-emitting lasers (VCSELs) with continuously graded mirror layers grown by MOCVD is reported. Continuous grading of the heterojunction interfaces in the heavily doped p-type distributed Bragg reflector (DBR) layers significantly reduced the diode resistance and self-heating, thus leading to higher power efficiencies, a wider CW current range, and a light output that is comparable to the MBE results. The VCSEL epilayer structure, grown by a low-pressure MOCVD system, is composed of an undoped four-quantum-well active layer structure bounded by Te-doped and C-doped DBR mirrors, containing 43.5 and 24 pairs of quarter-wave AlAs and AlGaAs layers, respectively. >

Ping Zhou

Papers

High temperature pulsed and continuous-wave operation and thermally stable threshold characteristics of vertical-cavity surface-emitting lasers grown by metalorganic chemical vapor deposition

High‐performance latchable optical switch and logic gates based on the integration of surface‐emitting lasers and photothyristors

Surface‐emitting laser‐based optical bistable switching device

Low series resistance continuously graded mirror multiple quantum-well vertical-cavity surface-emitting lasers grown by MOCVD

MOCVD growth of vertical cavity surface-emitting lasers with graded-composition mirrors