Yichun Yin

Two‐dimensional electron gas effects in the electromodulation spectra of a pseudomorphic Ga0.78Al0.22As/In0.21Ga0.79As/GaAs modulation‐doped quantum well structure

We have studied the electroreflectance and photoreflectance spectra from a pseudomorphic Ga0.78Al0.22As/In0.21Ga0.79As/GaAs modulation‐doped quantum well (MDQW) structure in the temperature range 79<T<304 K. The features from the InGaAs MDQW can be accounted for on the basis of a two‐dimensional density of states and a Fermi level filling factor. A detailed line shape fit makes it possible to evaluate the Fermi energy, and hence the two‐dimensional electron gas concentration (Ns), as well as other important parameters of the structure. Our value for Ns is in good agreement with a Hall measurement.

Analyzing semiconductor devices using modulation spectroscopy

Improvements in the quality and yield of semiconductor devices will rely on characterization methods that are informative, nondestructive, convenient, easy to use, and inexpensive. Ideally, one would like to perform the characterization procedure at room temperature on entire wafers, possibly even before the structure is removed from the growth chamber. Because of their simplicity and proven ability, the contactless electro-modulation methods of photoreflectance and contactless electroreflectance are ideally suited for this purpose. Modulation spectroscopy has already been applied to examine such devices as heterojunction bipolar transistors, pseudomorphic high-electron-mobility transistors, quantum-well lasers, vertical cavity surface-emitting lasers, multiple-quantum-well infrared detectors, superlattice optical mirrors, resonant tunneling structures, solar cells, and metal-oxide-semiconductor configurations.

Piezoreflectance of strained Si/Ge superlattices grown on Ge(001)

Abstract We have studied the piezoreflectance (PzR) and photoreflectance (PR) spectra at 77 K of a series of short-period Si/Ge superlattices grown on Ge(001) substrates. These samples are similar to those measured using electroreflectance (40 K) by Pearsall et al. [Phys. Rev. Lett. 63 (1989) 2104]. We have observed several low-energy features in the PzR data just above the direct band gap of Ge. They are clearly due to quantum-confined direct transitions in the Ge spacer region, not pseudodirect transitions in the short-period Si/Ge portion of the samples as reported by Pearsall et al.

Characterization of semiconductor device structures by modulation spectroscopy

This paper reviews the use of modulation spectroscopy for the characterization of a wide variety of semiconductor device structures. Some systems that will be discussed include pseudomorphic GaAlAs/InGaAs/GaAs modulation-doped quantum-well high-electron-mobility transistors (including the 300K determination of the 2D electron gas density), GaAlAs/GaAs, InP/InGaAs, InGaP/GaAs, InAlAs/InGaAs, and InGaAs/GaAs heterojunction bipolar transistors (including the determination of the built-in fields/doping levels in the emitter and collector regions), GaAs/GaAlAs quantum well IR detectors, quantum well lasers, etc. Particular attention will be paid to nondestructive, contactless techniques such as photoreflectance and contactless electroreflectance that can be performed on entire wafers.

Two-dimensional electron gas effects in the electromodulation spectra from a pseudomorphic GaAlAs/InGaAs/GaAs modulation-doped quantum well structure

The two-dimensional electron gas in a GaAlAs/InGaAs/GaAs modulation-doped quantum well was studied using contactless electroreflectance (17 K <T < 351 K) and photoluminescence (300 K). A many-body calculation of the electromodulation line shape, including observation of the Fermi edge transition up to 152 K, is in excellent agreement with experiment.

Electromodulation study of a pseudomorphic Ga0.78Al0.22As/In0.21Ga0.79As/GaAs modulation-doped quantum-well structure: two-dimensional electron gas effects

We have studied the electroreflectance and photoreflectance spectra from a pseudomorphic Ga0.78Al0.22As/In0.21Ga0.79As/GaAs modulation-doped quantum well (MDQW) structure in the temperature range 79 K < T < 304 K. The features from the InGaAs MDQW can be accounted for on the basis of a two-dimensional density of states and a Fermi level filling factor. A detailed lineshape fit makes it possible to evaluate the Fermi energy, and hence the two-dimensional electron gas concentration (Ns), as well as other important parameters of the structure. Our value for Ns is in good agreement with a Hall measurement. The effect of photo-injected carriers on Ns also was studied.

Contactless electromodulation for the characterization of semiconductor surfaces/interfaces

Modulation spectroscopy (particularly contactless modes) is a major tool for the study and characterization of semiconductor microstructures (quantum wells, superlattices, etc.), surfaces/interfaces (heterojunctions, semiconductor/vacuum, semiconductor/metal, semiconductor/electrolyte) and also for the evaluation of process-induced damage at surfaces/interfaces. In addition, it is also valuable for the characterization of device structures. A particularly useful form of modulation spectroscopy is electromodulation since it often yields the sharpest structure (third-derivative in the case of bulk/thin film material) and is sensitive to surface/interface electric fields. Furthermore, it can be performed in contactless modes [photoreflectance (PR) and contactless electroreflectance (CER)] that require no special mounting of the sample. This talk will discuss some recent applications of PR and CER to the characterization of a number of surfaces/interfaces.